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openvpn(8)		    System Manager's Manual		    openvpn(8)

       openvpn - secure	IP tunnel daemon.

       openvpn [ options ... ]

       OpenVPN	is  an open source VPN daemon by James Yonan.  Because OpenVPN
       tries to	be a universal VPN tool	offering a great deal of  flexibility,
       there are a lot of options on this manual page.	If you're new to Open-
       VPN, you	might want to skip ahead to the	 examples  section  where  you
       will  see how to	construct simple VPNs on the command line without even
       needing a configuration file.

       Also note that there's more documentation and examples on  the  OpenVPN
       web site:

       And  if you would like to see a shorter version of this manual, see the
       openvpn usage message which can be obtained by running openvpn  without
       any parameters.

       OpenVPN	is  a robust and highly	flexible VPN daemon.  OpenVPN supports
       SSL/TLS security,  ethernet  bridging,  TCP  or	UDP  tunnel  transport
       through	proxies	 or  NAT,  support  for	dynamic	IP addresses and DHCP,
       scalability to hundreds or thousands of users, and portability to  most
       major OS	platforms.

       OpenVPN	is  tightly  bound to the OpenSSL library, and derives much of
       its crypto capabilities from it.

       OpenVPN supports	conventional encryption	using a	pre-shared secret  key
       (Static	Key mode) or public key	security (SSL/TLS mode)	using client &
       server certificates.  OpenVPN also supports non-encrypted TCP/UDP  tun-

       OpenVPN	is designed to work with the TUN/TAP virtual networking	inter-
       face that exists	on most	platforms.

       Overall,	OpenVPN	aims to	offer many of the key features	of  IPSec  but
       with a relatively lightweight footprint.

       OpenVPN allows any option to be placed either on	the command line or in
       a configuration file.  Though all command line options are preceded  by
       a double-leading-dash ("--"), this prefix can be	removed	when an	option
       is placed in a configuration file.

       --help Show options.

       --config	file
	      Load additional config options from file where each line	corre-
	      sponds  to  one  command	line option, but with the leading '--'

	      If --config file is the only option to the openvpn command,  the
	      --config can be removed, and the command can be given as openvpn

	      Note that	configuration files can	 be  nested  to	 a  reasonable

	      Double  quotation	or single quotation characters ("", '')	can be
	      used to enclose single parameters	containing whitespace, and "#"
	      or ";" characters	in the first column can	be used	to denote com-

	      Note that	OpenVPN	2.0 and	higher performs	backslash-based	 shell
	      escaping for characters not in single quotations,	so the follow-
	      ing mappings should be observed:

		  \\	   Maps	to a single backslash character	(\).
		  \"	   Pass	a literal doublequote character	("), don't
			   interpret it	as enclosing a parameter.
		  \[SPACE] Pass	a literal space	or tab character, don't
			   interpret it	as a parameter delimiter.

	      For example on Windows,  use  double  backslashes	 to  represent

		  secret "c:\\OpenVPN\\secret.key"

	      For   examples   of   configuration   files,   see  http://open-

	      Here is an example configuration file:

		  # Sample OpenVPN configuration file for
		  # using a pre-shared static key.
		  # '#'	or ';' may be used to delimit comments.

		  # Use	a dynamic tun device.
		  dev tun

		  # Our	remote peer
		  remote mypeer.mydomain

		  # is	our local VPN endpoint
		  # is	our remote VPN endpoint

		  # Our	pre-shared static key
		  secret static.key

   Tunnel Options:
       --mode m
	      Set OpenVPN major	mode.  By default, OpenVPN runs	 in  point-to-
	      point   mode   ("p2p").	OpenVPN	 2.0  introduces  a  new  mode
	      ("server") which implements a multi-client server	capability.

       --local host
	      Local host name or IP address for	bind.  If  specified,  OpenVPN
	      will  bind  to  this address only.  If unspecified, OpenVPN will
	      bind to all interfaces.

       --remote	host [port] [proto]
	      Remote host  name	 or  IP	 address.   On	the  client,  multiple
	      --remote options may be specified	for redundancy,	each referring
	      to a different OpenVPN  server.	Specifying  multiple  --remote
	      options  for  this purpose is a special case of the more general
	      connection-profile feature.  See the <connection>	 documentation

	      The  OpenVPN client will try to connect to a server at host:port
	      in the order specified by	the list of --remote options.

	      proto indicates the protocol to use  when	 connecting  with  the
	      remote, and may be "tcp" or "udp".

	      The  client  will	 move  on to the next host in the list,	in the
	      event of connection failure.  Note that at any given  time,  the
	      OpenVPN client will at most be connected to one server.

	      Note  that  since	 UDP  is connectionless, connection failure is
	      defined by the --ping and	--ping-restart options.

	      Note the following corner	case:  If you  use  multiple  --remote
	      options, AND you are dropping root privileges on the client with
	      --user and/or --group, AND the client is running	a  non-Windows
	      OS,  if  the  client  needs to switch to a different server, and
	      that server pushes back different	TUN/TAP	or route settings, the
	      client may lack the necessary privileges to close	and reopen the
	      TUN/TAP interface.  This could cause the client to exit  with  a
	      fatal error.

	      If --remote is unspecified, OpenVPN will listen for packets from
	      any IP address, but will not act on those	 packets  unless  they
	      pass all authentication tests.  This requirement for authentica-
	      tion is binding on all potential peers, even  those  from	 known
	      and  supposedly trusted IP addresses (it is very easy to forge a
	      source IP	address	on a UDP packet).

	      When used	in TCP mode, --remote will act as a filter,  rejecting
	      connections from any host	which does not match host.

	      If  host	is a DNS name which resolves to	multiple IP addresses,
	      the first	address	returned by the	system getaddrinfo()  function
	      will  be used (no	DNS randomization inside OpenVPN 2.3.x,	and it
	      will not try multiple addresses).

	      Prepend a	random string (6 bytes,	12 hex characters) to hostname
	      to  prevent  DNS	caching.   For example,	"" would be
	      modified to "<random-chars>".

	      Define a client connection profile.  Client connection  profiles
	      are  groups of OpenVPN options that describe how to connect to a
	      given OpenVPN server.  Client connection profiles	are  specified
	      within an	OpenVPN	configuration file, and	each profile is	brack-
	      eted by <connection> and </connection>.

	      An OpenVPN client	will try each connection profile  sequentially
	      until it achieves	a successful connection.

	      --remote-random  can be used to initially	"scramble" the connec-
	      tion list.

	      Here is an example of connection profile usage:

		  dev tun

		  remote 1194 udp

		  remote 443 tcp

		  remote 443 tcp
		  http-proxy 8080

		  remote 443 tcp
		  http-proxy 8080

		  pkcs12 client.p12
		  ns-cert-type server
		  verb 3

	      First we try to connect to a server at	 using
	      UDP.   If	that fails, we then try	to connect to
	      using TCP.  If that also fails, then try connecting  through  an
	      HTTP  proxy  at	to using TCP.
	      Finally, try to connect through the same proxy to	 a  server  at using TCP.

	      The  following  OpenVPN options may be used inside of a <connec-
	      tion> block:

	      bind,   connect-retry,	connect-retry-max,    connect-timeout,
	      explicit-exit-notify,  float,  fragment, http-proxy, http-proxy-
	      option, http-proxy-retry,	http-proxy-timeout,  link-mtu,	local,
	      lport,  mssfix,  mtu-disc,  nobind,  port, proto,	remote,	rport,
	      socks-proxy, socks-proxy-retry, tun-mtu and tun-mtu-extra.

	      A	defaulting mechanism exists for	specifying options to apply to
	      all  <connection>	 profiles.   If	any of the above options (with
	      the exception of remote  )  appear  outside  of  a  <connection>
	      block,  but  in a	configuration file which has one or more <con-
	      nection> blocks, the option setting will be used	as  a  default
	      for  <connection>	 blocks	 which	follow it in the configuration

	      For example, suppose the nobind option were placed in the	sample
	      configuration  file  above, near the top of the file, before the
	      first <connection> block.	 The effect would be as	if nobind were
	      declared in all <connection> blocks below	it.

       --proto-force p
	      When  iterating  through connection profiles, only consider pro-
	      files using protocol p ('tcp'|'udp').

	      When multiple --remote address/ports are specified, or  if  con-
	      nection  profiles	 are being used, initially randomize the order
	      of the list as a kind of basic load-balancing measure.

       --proto p
	      Use protocol p for communicating with remote  host.   p  can  be
	      udp, tcp-client, or tcp-server.

	      The default protocol is udp when --proto is not specified.

	      For  UDP	operation,  --proto  udp  should  be specified on both

	      For TCP operation, one peer must use --proto tcp-server and  the
	      other  must  use	--proto	 tcp-client.  A	peer started with tcp-
	      server will wait indefinitely for	 an  incoming  connection.   A
	      peer  started  with  tcp-client  will attempt to connect,	and if
	      that fails, will sleep for 5 seconds (adjustable via the	--con-
	      nect-retry  option)  and	try  again infinite or up to N retries
	      (adjustable  via	the  --connect-retry-max  option).   Both  TCP
	      client  and  server  will	 simulate  a SIGUSR1 restart signal if
	      either side resets the connection.

	      OpenVPN is designed to operate optimally over UDP, but TCP capa-
	      bility  is provided for situations where UDP cannot be used.  In
	      comparison with UDP, TCP will usually be somewhat	less efficient
	      and less robust when used	over unreliable	or congested networks.

	      This  article  outlines  some of problems	with tunneling IP over

	      There are	certain	cases, however,	where using TCP	may be	advan-
	      tageous from a security and robustness perspective, such as tun-
	      neling non-IP or application-level UDP protocols,	 or  tunneling
	      protocols	which don't possess a built-in reliability layer.

       --connect-retry n
	      For  --proto tcp-client, take n as the number of seconds to wait
	      between connection retries (default=5).

       --connect-timeout n
	      For --proto tcp-client, set  connection  timeout	to  n  seconds

       --connect-retry-max n
	      For  --proto tcp-client, take n as the number of retries of con-
	      nection attempt (default=infinite).

	      Show sensed HTTP or SOCKS	proxy settings.	Currently,  only  Win-
	      dows clients support this	option.

       --http-proxy server port	[authfile|'auto'|'auto-nct'] [auth-method]
	      Connect  to  remote host through an HTTP proxy at	address	server
	      and port port.  If HTTP Proxy-Authenticate is required, authfile
	      is  a  file  containing  a  username and password	on 2 lines, or
	      "stdin" to prompt	from console.

	      auth-method should be one	of "none", "basic", or "ntlm".

	      HTTP Digest authentication is supported as well,	but  only  via
	      the auto or auto-nct flags (below).

	      The  auto	 flag  causes  OpenVPN	to automatically determine the
	      auth-method and query stdin  or  the  management	interface  for
	      username/password	credentials, if	required.  This	flag exists on
	      OpenVPN 2.1 or higher.

	      The auto-nct flag	(no  clear-text	 auth)	instructs  OpenVPN  to
	      automatically determine the authentication method, but to	reject
	      weak authentication protocols such as HTTP Basic Authentication.

	      Retry indefinitely on HTTP proxy errors.	If an HTTP proxy error
	      occurs, simulate a SIGUSR1 reset.

       --http-proxy-timeout n
	      Set proxy	timeout	to n seconds, default=5.

       --http-proxy-option type	[parm]
	      Set  extended  HTTP  proxy  options.   Repeat  to	 set  multiple

	      VERSION  version	--  Set	 HTTP  version	 number	  to   version

	      AGENT user-agent -- Set HTTP "User-Agent"	string to user-agent.

       --socks-proxy server [port] [authfile]
	      Connect  to remote host through a	Socks5 proxy at	address	server
	      and port port (default=1080).  authfile  (optional)  is  a  file
	      containing  a  username  and  password on	2 lines, or "stdin" to
	      prompt from console.

	      Retry indefinitely on Socks proxy	 errors.   If  a  Socks	 proxy
	      error occurs, simulate a SIGUSR1 reset.

       --resolv-retry n
	      If hostname resolve fails	for --remote, retry resolve for	n sec-
	      onds before failing.

	      Set n to "infinite" to retry indefinitely.

	      By default, --resolv-retry infinite is enabled.  You can disable
	      by setting n=0.

	      Allow  remote  peer to change its	IP address and/or port number,
	      such as due to DHCP (this	is the	default	 if  --remote  is  not
	      used).   --float	when specified with --remote allows an OpenVPN
	      session to initially connect to a	peer at	a known	address,  how-
	      ever if packets arrive from a new	address	and pass all authenti-
	      cation tests, the	new address will take control of the  session.
	      This  is	useful when you	are connecting to a peer which holds a
	      dynamic address such as a	dial-in	user or	DHCP client.

	      Essentially, --float tells OpenVPN to accept authenticated pack-
	      ets  from	 any address, not only the address which was specified
	      in the --remote option.

       --ipchange cmd
	      Run command cmd when our remote ip-address is initially  authen-
	      ticated or changes.

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      When cmd is executed two arguments are appended after any	 argu-
	      ments specified in cmd , as follows:

	      cmd ip_address port_number

	      Don't use	--ipchange in --mode server mode.  Use a --client-con-
	      nect script instead.

	      See the "Environmental Variables"	section	below  for  additional
	      parameters passed	as environmental variables.

	      If you are running in a dynamic IP address environment where the
	      IP addresses of either peer could	change without notice, you can
	      use  this	 script, for example, to edit the /etc/hosts file with
	      the current address of the peer.	The script will	be  run	 every
	      time the remote peer changes its IP address.

	      Similarly	 if our	IP address changes due to DHCP,	we should con-
	      figure our IP address change script (see man page	for  dhcpcd(8)
	      )	 to  deliver  a	 SIGHUP	or SIGUSR1 signal to OpenVPN.  OpenVPN
	      will then	 reestablish  a	 connection  with  its	most  recently
	      authenticated peer on its	new IP address.

       --port port
	      TCP/UDP port number or port name for both	local and remote (sets
	      both --lport and --rport options to given	 port).	  The  current
	      default of 1194 represents the official IANA port	number assign-
	      ment for OpenVPN and has been  used  since  version  2.0-beta17.
	      Previous versions	used port 5000 as the default.

       --lport port
	      Set  local TCP/UDP port number or	name.  Cannot be used together
	      with --nobind option.

       --rport port
	      Set TCP/UDP port number or name used by the --remote option. The
	      port can also be set directly using the --remote option.

       --bind Bind  to	local address and port.	This is	the default unless any
	      of --proto tcp-client , --http-proxy or --socks-proxy are	used.

	      Do not bind to local address and port.  The IP stack will	 allo-
	      cate  a  dynamic port for	returning packets.  Since the value of
	      the dynamic port could not be known in advance by	a  peer,  this
	      option  is only suitable for peers which will be initiating con-
	      nections by using	the --remote option.

       --dev tunX | tapX | null
	      TUN/TAP virtual network device ( X can be	omitted	for a  dynamic

	      See  examples  section  below for	an example on setting up a TUN

	      You must use either tun devices on both ends of  the  connection
	      or  tap devices on both ends.  You cannot	mix them, as they rep-
	      resent different underlying network layers.

	      tun devices encapsulate IPv4 or IPv6 (OSI	 Layer	3)  while  tap
	      devices encapsulate Ethernet 802.3 (OSI Layer 2).

       --dev-type device-type
	      Which  device type are we	using?	device-type should be tun (OSI
	      Layer 3) or tap (OSI Layer 2).  Use  this	 option	 only  if  the
	      TUN/TAP device used with --dev does not begin with tun or	tap.

       --topology mode
	      Configure	 virtual addressing topology when running in --dev tun
	      mode.  This directive has	no meaning in --dev  tap  mode,	 which
	      always uses a subnet topology.

	      If  you  set  this  directive  on	 the  server, the --server and
	      --server-bridge directives will automatically push  your	chosen
	      topology setting to clients as well.  This directive can also be
	      manually pushed to clients.   Like  the  --dev  directive,  this
	      directive	must always be compatible between client and server.

	      mode can be one of:

	      net30  --	 Use  a	point-to-point topology, by allocating one /30
	      subnet per client.  This is  designed  to	 allow	point-to-point
	      semantics	 when  some  or	all of the connecting clients might be
	      Windows systems.	This is	the default on OpenVPN 2.0.

	      p2p -- Use a point-to-point topology where the  remote  endpoint
	      of  the  client's	 tun interface always points to	the local end-
	      point of the server's tun	interface.  This mode allocates	a sin-
	      gle IP address per connecting client.  Only use when none	of the
	      connecting clients are Windows systems.  This mode is  function-
	      ally equivalent to the --ifconfig-pool-linear directive which is
	      available	in OpenVPN 2.0 and is now deprecated.

	      subnet --	Use a subnet rather than a point-to-point topology  by
	      configuring the tun interface with a local IP address and	subnet
	      mask, similar to the topology used in  --dev  tap	 and  ethernet
	      bridging mode.  This mode	allocates a single IP address per con-
	      necting client and works on Windows  as  well.   Only  available
	      when  server  and	 clients are OpenVPN 2.1 or higher, or OpenVPN
	      2.0.x which has been manually patched with the --topology	direc-
	      tive code.  When used on Windows,	requires version 8.2 or	higher
	      of the TAP-Win32 driver.	When used on *nix, requires  that  the
	      tun  driver  supports an ifconfig(8) command which sets a	subnet
	      instead of a remote endpoint IP address.

	      This option exists in OpenVPN 2.1	or higher.

	      Note: Using --topology subnet changes the	interpretation of  the
	      arguments	 of  --ifconfig	 to  mean "address netmask", no	longer
	      "local remote".

	      Build a tun link capable of forwarding IPv6 traffic.  Should  be
	      used  in	conjunction  with  --dev tun or	--dev tunX.  A warning
	      will be displayed	if no specific IPv6 TUN	support	 for  your  OS
	      has been compiled	into OpenVPN.

	      See below	for further IPv6-related configuration options.

       --dev-node node
	      Explicitly  set  the device node rather than using /dev/net/tun,
	      /dev/tun,	/dev/tap, etc.	If OpenVPN cannot figure  out  whether
	      node  is	a TUN or TAP device based on the name, you should also
	      specify --dev-type tun or	--dev-type tap.

	      Under Mac	OS X this option can be	used to	 specify  the  default
	      tun  implementation.  Using  --dev-node utun forces usage	of the
	      native Darwin tun	kernel support.	Use --dev-node utunN to	select
	      a	  specific   utun   instance.  To  force  using	 the  tun.kext
	      (/dev/tunX)  use	--dev-node  tun.   When	  not	specifying   a
	      --dev-node  option openvpn will first try	to open	utun, and fall
	      back to tun.kext.

	      On Windows systems, select the TAP-Win32 adapter which is	 named
	      node in the Network Connections Control Panel or the raw GUID of
	      the adapter enclosed  by	braces.	  The  --show-adapters	option
	      under  Windows  can also be used to enumerate all	available TAP-
	      Win32 adapters and will show both	the network  connections  con-
	      trol panel name and the GUID for each TAP-Win32 adapter.

       --lladdr	address
	      Specify  the  link layer address,	more commonly known as the MAC
	      address.	Only applied to	TAP devices.

       --iproute cmd
	      Set alternate command to execute	instead	 of  default  iproute2
	      command.	 May  be  used in order	to execute OpenVPN in unprivi-
	      leged environment.

       --ifconfig l rn
	      Set TUN/TAP adapter parameters.  l is  the  IP  address  of  the
	      local  VPN endpoint.  For	TUN devices in point-to-point mode, rn
	      is the IP	address	of the remote VPN endpoint.  For TAP  devices,
	      or  TUN  devices	used  with --topology subnet, rn is the	subnet
	      mask of the virtual network segment which	is  being  created  or
	      connected	to.

	      For TUN devices, which facilitate	virtual	point-to-point IP con-
	      nections (when used in --topology	net30 or p2p mode), the	proper
	      usage of --ifconfig is to	use two	private	IP addresses which are
	      not a member of any existing subnet which	is  in	use.   The  IP
	      addresses	 may  be  consecutive  and  should  have  their	 order
	      reversed on the remote peer.  After the VPN is  established,  by
	      pinging rn, you will be pinging across the VPN.

	      For  TAP	devices,  which	 provide the ability to	create virtual
	      ethernet segments, or TUN	 devices  in  --topology  subnet  mode
	      (which create virtual "multipoint	networks"), --ifconfig is used
	      to set an	IP address and subnet mask just	as a physical ethernet
	      adapter would be similarly configured.  If you are attempting to
	      connect to a remote ethernet bridge, the IP address  and	subnet
	      should  be set to	values which would be valid on the the bridged
	      ethernet segment (note also that DHCP can	be used	for  the  same

	      This  option,  while  primarily a	proxy for the ifconfig(8) com-
	      mand, is designed	to simplify TUN/TAP  tunnel  configuration  by
	      providing	 a standard interface to the different ifconfig	imple-
	      mentations on different platforms.

	      --ifconfig parameters which are IP addresses can also be	speci-
	      fied as a	DNS or /etc/hosts file resolvable name.

	      For TAP devices, --ifconfig should not be	used if	the TAP	inter-
	      face will	be getting an IP address lease from a DHCP server.

	      Don't actually execute  ifconfig/netsh  commands,	 instead  pass
	      --ifconfig parameters to scripts using environmental variables.

	      Don't  output  an	 options  consistency  check  warning  if  the
	      --ifconfig option	on this	side of	the connection	doesn't	 match
	      the  remote  side.   This	 is useful when	you want to retain the
	      overall benefits of the  options	consistency  check  (also  see
	      --disable-occ  option)  while only disabling the ifconfig	compo-
	      nent of the check.

	      For example, if you have a configuration where  the  local  host
	      uses  --ifconfig	but  the  remote  host	does not, use --ifcon-
	      fig-nowarn on the	local host.

	      This option will also silence warnings about  potential  address
	      conflicts	 which	occasionally  annoy  more experienced users by
	      triggering "false	positive" warnings.

       --route network/IP [netmask] [gateway] [metric]
	      Add route	to routing  table  after  connection  is  established.
	      Multiple	routes can be specified.  Routes will be automatically
	      torn down	in reverse order prior to TUN/TAP device close.

	      This option is intended as a convenience proxy for the  route(8)
	      shell  command, while at the same	time providing portable	seman-
	      tics across OpenVPN's platform space.

	      netmask default --

	      gateway default -- taken	from  --route-gateway  or  the	second
	      parameter	to --ifconfig when --dev tun is	specified.

	      metric default --	taken from --route-metric otherwise 0.

	      The  default can be specified by leaving an option blank or set-
	      ting it to "default".

	      The network and gateway parameters can also be  specified	 as  a
	      DNS  or /etc/hosts file resolvable name, or as one of three spe-
	      cial keywords:

	      vpn_gateway -- The remote	VPN endpoint address  (derived	either
	      from  --route-gateway or the second parameter to --ifconfig when
	      --dev tun	is specified).

	      net_gateway -- The pre-existing IP default  gateway,  read  from
	      the routing table	(not supported on all OSes).

	      remote_host  --  The --remote address if OpenVPN is being	run in
	      client mode, and is undefined in server mode.

       --max-routes n
	      Allow a maximum number of	n --route  options  to	be  specified,
	      either  in the local configuration file, or pulled from an Open-
	      VPN server.  By default, n=100.

       --route-gateway gw|'dhcp'
	      Specify a	default	gateway	gw for use with	--route.

	      If dhcp is specified as the parameter, the gateway address  will
	      be  extracted  from  a DHCP negotiation with the OpenVPN server-
	      side LAN.

       --route-metric m
	      Specify a	default	metric m for use with --route.

       --route-delay [n] [w]
	      Delay n  seconds	(default=0)  after  connection	establishment,
	      before  adding  routes.  If n is 0, routes will be added immedi-
	      ately upon connection establishment.  If --route-delay is	 omit-
	      ted,  routes will	be added immediately after TUN/TAP device open
	      and --up script execution, before	any --user or  --group	privi-
	      lege downgrade (or --chroot execution.)

	      This  option is designed to be useful in scenarios where DHCP is
	      used to set tap adapter addresses.  The delay will give the DHCP
	      handshake	time to	complete before	routes are added.

	      On  Windows, --route-delay tries to be more intelligent by wait-
	      ing w seconds (w=30 by default) for  the	TAP-Win32  adapter  to
	      come up before adding routes.

       --route-up cmd
	      Run   command   cmd   after   routes   are   added,  subject  to

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      See  the	"Environmental Variables" section below	for additional
	      parameters passed	as environmental variables.

       --route-pre-down	cmd
	      Run command cmd before routes are	removed	upon disconnection.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      See  the	"Environmental Variables" section below	for additional
	      parameters passed	as environmental variables.

	      Don't add	or remove routes automatically.	 Instead  pass	routes
	      to --route-up script using environmental variables.

	      When  used  with	--client  or  --pull, accept options pushed by
	      server EXCEPT for	routes,	 block-outside-dns  and	 dhcp  options
	      like DNS servers.

	      When used	on the client, this option effectively bars the	server
	      from adding routes to the	client's routing table,	 however  note
	      that this	option still allows the	server to set the TCP/IP prop-
	      erties of	the client's TUN/TAP interface.

	      Allow client to pull DNS names from server  (rather  than	 being
	      limited	to   IP	  address)   for   --ifconfig,	 --route,  and

       --client-nat snat|dnat network netmask alias
	      This pushable client option sets up a stateless  one-to-one  NAT
	      rule  on	packet	addresses  (not	ports),	and is useful in cases
	      where routes or ifconfig settings	pushed	to  the	 client	 would
	      create an	IP numbering conflict.

	      network/netmask  (for  example defines
	      the local	view of	a resource from	the client perspective,	 while
	      alias/netmask  (for  example defines the
	      remote view from the server perspective.

	      Use snat (source NAT) for	resources owned	by the client and dnat
	      (destination NAT)	for remote resources.

	      Set  --verb  6  for debugging info showing the transformation of
	      src/dest addresses in packets.

       --redirect-gateway flags...
	      Automatically execute routing commands to	cause all outgoing  IP
	      traffic  to  be  redirected over the VPN.	 This is a client-side

	      This option performs three steps:

	      (1) Create a static route	for the	--remote  address  which  for-
	      wards to the pre-existing	default	gateway.  This is done so that
	      (3) will not create a routing loop.

	      (2) Delete the default gateway route.

	      (3) Set the new default gateway to be the	VPN  endpoint  address
	      (derived	either from --route-gateway or the second parameter to
	      --ifconfig when --dev tun	is specified).

	      When the tunnel is  torn	down,  all  of	the  above  steps  are
	      reversed so that the original default route is restored.

	      Option flags:

	      local -- Add the local flag if both OpenVPN servers are directly
	      connected	via a common subnet, such as with wireless.  The local
	      flag will	cause step 1 above to be omitted.

	      autolocal	 --  Try  to automatically determine whether to	enable
	      local flag above.

	      def1 -- Use this flag to override	the default gateway  by	 using	 and rather than  This has the
	      benefit of overriding but	not wiping out	the  original  default

	      bypass-dhcp  --  Add a direct route to the DHCP server (if it is
	      non-local) which	bypasses  the  tunnel  (Available  on  Windows
	      clients, may not be available on non-Windows clients).

	      bypass-dns  --  Add a direct route to the	DNS server(s) (if they
	      are non-local) which bypasses the	tunnel (Available  on  Windows
	      clients, may not be available on non-Windows clients).

	      block-local  --  Block  access  to  local	LAN when the tunnel is
	      active, except for the LAN gateway itself.  This is accomplished
	      by  routing  the	local LAN (except for the LAN gateway address)
	      into the tunnel.

       --link-mtu n
	      Sets an upper bound on the size of UDP packets  which  are  sent
	      between  OpenVPN	peers.	 It's  best  not to set	this parameter
	      unless you know what you're doing.

       --redirect-private [flags]
	      Like --redirect-gateway, but omit	actually changing the  default
	      gateway.	Useful when pushing private subnets.

       --tun-mtu n
	      Take  the	TUN device MTU to be n and derive the link MTU from it
	      (default=1500).  In most cases, you will probably	want to	 leave
	      this parameter set to its	default	value.

	      The  MTU	(Maximum  Transmission	Units) is the maximum datagram
	      size in bytes that can be	sent unfragmented  over	 a  particular
	      network  path.   OpenVPN requires	that packets on	the control or
	      data channels be sent unfragmented.

	      MTU problems often manifest themselves as	connections which hang
	      during periods of	active usage.

	      It's  best to use	the --fragment and/or --mssfix options to deal
	      with MTU sizing issues.

       --tun-mtu-extra n
	      Assume that the TUN/TAP device might return as many as  n	 bytes
	      more  than  the --tun-mtu	size on	read.  This parameter defaults
	      to 0, which is sufficient	for most TUN devices.  TAP devices may
	      introduce	 additional  overhead in excess	of the MTU size, and a
	      setting of 32 is the default when	TAP devices  are  used.	  This
	      parameter	only controls internal OpenVPN buffer sizing, so there
	      is no transmission  overhead  associated	with  using  a	larger

       --mtu-disc type
	      Should  we  do Path MTU discovery	on TCP/UDP channel?  Only sup-
	      ported on	OSes such as Linux that	supports the necessary	system
	      call to set.

	      'no' -- Never send DF (Don't Fragment) frames
	      'maybe' -- Use per-route hints
	      'yes' -- Always DF (Don't	Fragment)

	      To  empirically  measure	MTU  on	 connection  startup,  add the
	      --mtu-test option	to your	configuration.	OpenVPN	will send ping
	      packets  of  various  sizes  to  the remote peer and measure the
	      largest  packets	which	were   successfully   received.	   The
	      --mtu-test process normally takes	about 3	minutes	to complete.

       --fragment max
	      Enable  internal datagram	fragmentation so that no UDP datagrams
	      are sent which are larger	than max bytes.

	      The max  parameter  is  interpreted  in  the  same  way  as  the
	      --link-mtu  parameter, i.e. the UDP packet size after encapsula-
	      tion overhead has	been added  in,	 but  not  including  the  UDP
	      header itself.

	      The  --fragment  option  only makes sense	when you are using the
	      UDP protocol ( --proto udp ).

	      --fragment adds 4	bytes of overhead per datagram.

	      See the --mssfix option below for	an important related option to

	      It should	also be	noted that this	option is not meant to replace
	      UDP fragmentation	at the IP stack	level.	It is only meant as  a
	      last  resort  when  path	MTU  discovery	is broken.  Using this
	      option is	less efficient than fixing path	MTU discovery for your
	      IP link and using	native IP fragmentation	instead.

	      Having  said that, there are circumstances where using OpenVPN's
	      internal fragmentation capability	may be your only option,  such
	      as  tunneling  a	UDP multicast stream which requires fragmenta-

       --mssfix	max
	      Announce to TCP sessions	running	 over  the  tunnel  that  they
	      should limit their send packet sizes such	that after OpenVPN has
	      encapsulated them, the resulting UDP packet  size	 that  OpenVPN
	      sends  to	 its peer will not exceed max bytes. The default value
	      is 1450.

	      The max  parameter  is  interpreted  in  the  same  way  as  the
	      --link-mtu  parameter, i.e. the UDP packet size after encapsula-
	      tion overhead has	been added  in,	 but  not  including  the  UDP
	      header itself. Resulting packet would be at most 28 bytes	larger
	      for IPv4 and 48 bytes for	IPv6 (20/40 bytes for IP header	and  8
	      bytes for	UDP header). Default value of 1450 allows IPv4 packets
	      to be transmitted	over a link with MTU 1473 or higher without IP
	      level fragmentation.

	      The  --mssfix option only	makes sense when you are using the UDP
	      protocol for OpenVPN peer-to-peer	communication,	i.e.   --proto

	      --mssfix	and  --fragment	 can  be  ideally used together, where
	      --mssfix will try	to keep	TCP from needing packet	 fragmentation
	      in the first place, and if big packets come through anyhow (from
	      protocols	other than TCP), --fragment will  internally  fragment

	      Both  --fragment	and --mssfix are designed to work around cases
	      where Path MTU discovery is broken on the	network	 path  between
	      OpenVPN peers.

	      The  usual  symptom of such a breakdown is an OpenVPN connection
	      which successfully starts, but then stalls during	active usage.

	      If --fragment and	--mssfix are used together, --mssfix will take
	      its default max parameter	from the --fragment max	option.

	      Therefore,  one  could lower the maximum UDP packet size to 1300
	      (a good first try	for solving MTU-related	 connection  problems)
	      with the following options:

	      --tun-mtu	1500 --fragment	1300 --mssfix

       --sndbuf	size
	      Set  the TCP/UDP socket send buffer size.	 Defaults to operation
	      system default.

       --rcvbuf	size
	      Set the TCP/UDP socket receive buffer size.  Defaults to	opera-
	      tion system default.

       --mark value
	      Mark encrypted packets being sent	with value. The	mark value can
	      be matched in policy routing and packetfilter rules. This	option
	      is  only	supported in Linux and does nothing on other operating

       --socket-flags flags...
	      Apply the	given flags to the  OpenVPN  transport	socket.	  Cur-
	      rently, only TCP_NODELAY is supported.

	      The  TCP_NODELAY	socket	flag is	useful in TCP mode, and	causes
	      the kernel to send tunnel	packets	immediately over the TCP  con-
	      nection  without	trying to group	several	smaller	packets	into a
	      larger packet.  This can result in a considerably	improvement in

	      This  option  is	pushable  from server to client, and should be
	      used on both client and server for maximum effect.

       --txqueuelen n
	      (Linux only) Set the TX queue length on the  TUN/TAP  interface.
	      Currently	defaults to 100.

       --shaper	n
	      Limit bandwidth of outgoing tunnel data to n bytes per second on
	      the TCP/UDP port.	 Note that this	will only work if mode is  set
	      to  p2p.	If you want to limit the bandwidth in both directions,
	      use this option on both peers.

	      OpenVPN uses the following algorithm to implement	traffic	 shap-
	      ing: Given a shaper rate of n bytes per second, after a datagram
	      write of b bytes is queued on the	TCP/UDP	port, wait  a  minimum
	      of (b / n) seconds before	queuing	the next write.

	      It  should  be  noted  that  OpenVPN  supports  multiple tunnels
	      between the same two peers, allowing you to construct full-speed
	      and reduced bandwidth tunnels at the same	time, routing low-pri-
	      ority data such as off-site backups over the  reduced  bandwidth
	      tunnel, and other	data over the full-speed tunnel.

	      Also  note  that for low bandwidth tunnels (under	1000 bytes per
	      second), you should probably use lower MTU values	as  well  (see
	      above),  otherwise  the  packet latency will grow	so large as to
	      trigger timeouts in the TLS layer	and  TCP  connections  running
	      over the tunnel.

	      OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.

       --inactive n [bytes]
	      Causes  OpenVPN  to  exit	 after	n seconds of inactivity	on the
	      TUN/TAP device. The time length of inactivity is measured	 since
	      the  last	incoming or outgoing tunnel packet.  The default value
	      is 0 seconds, which disables this	feature.

	      If the optional bytes parameter is included, exit	if  less  than
	      bytes  of	 combined  in/out  traffic are produced	on the tun/tap
	      device in	n seconds.

	      In any case, OpenVPN's internal ping  packets  (which  are  just
	      keepalives)  and	TLS control packets are	not considered "activ-
	      ity", nor	are they counted as traffic, as	they are  used	inter-
	      nally by OpenVPN and are not an indication of actual user	activ-

       --ping n
	      Ping remote over the TCP/UDP control channel if no packets  have
	      been  sent  for at least n seconds (specify --ping on both peers
	      to cause ping packets to be sent in both directions since	 Open-
	      VPN  ping	 packets  are  not echoed like IP ping packets).  When
	      used  in	one  of	 OpenVPN's  secure  modes   (where   --secret,
	      --tls-server,  or	 --tls-client  is  specified), the ping	packet
	      will be cryptographically	secure.

	      This option has two intended uses:

	      (1) Compatibility	with stateful firewalls.   The	periodic  ping
	      will  ensure  that a stateful firewall rule which	allows OpenVPN
	      UDP packets to pass will not time	out.

	      (2) To provide a basis for the remote to test the	 existence  of
	      its peer using the --ping-exit option.

       --ping-exit n
	      Causes OpenVPN to	exit after n seconds pass without reception of
	      a	ping or	other packet from remote.  This	option can be combined
	      with  --inactive,	--ping,	and --ping-exit	to create a two-tiered
	      inactivity disconnect.

	      For example,

	      openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60

	      when used	on both	peers will cause OpenVPN  to  exit  within  60
	      seconds if its peer disconnects, but will	exit after one hour if
	      no actual	tunnel data is exchanged.

       --ping-restart n
	      Similar to --ping-exit, but trigger a SIGUSR1  restart  after  n
	      seconds  pass  without  reception	of a ping or other packet from

	      This option is useful in cases  where  the  remote  peer	has  a
	      dynamic  IP  address and a low-TTL DNS name is used to track the
	      IP address using	a  service  such  as  +  a
	      dynamic DNS client such as ddclient.

	      If  the  peer  cannot  be	 reached, a restart will be triggered,
	      causing the hostname used	with --remote to  be  re-resolved  (if
	      --resolv-retry is	also specified).

	      In server	mode, --ping-restart, --inactive, or any other type of
	      internally generated signal will always be applied to individual
	      client  instance	objects,  never	 to whole server itself.  Note
	      also in server mode that any internally generated	 signal	 which
	      would  normally  cause a restart,	will cause the deletion	of the
	      client instance object instead.

	      In client	mode, the --ping-restart parameter is set to 120  sec-
	      onds  by default.	 This default will hold	until the client pulls
	      a	replacement value from the server, based  on  the  --keepalive
	      setting  in the server configuration.  To	disable	the 120	second
	      default, set --ping-restart 0 on the client.

	      See the signals section below for	more information on SIGUSR1.

	      Note that	the behavior of	SIGUSR1	can be modified	by the	--per-
	      sist-tun,	   --persist-key,   --persist-local-ip,	  and	--per-
	      sist-remote-ip options.

	      Also note	 that  --ping-exit  and	 --ping-restart	 are  mutually
	      exclusive	and cannot be used together.

       --keepalive n m
	      A	helper directive designed to simplify the expression of	--ping
	      and --ping-restart in server mode	configurations.

	      The server timeout is set	twice the value	of  the	 second	 argu-
	      ment.   This  ensures  that a timeout is detected	on client side
	      before the server	side drops the connection.

	      For example, --keepalive 10 60 expands as	follows:

		   if mode server:
		     ping 10
		     ping-restart 120
		     push "ping	10"
		     push "ping-restart	60"
		     ping 10
		     ping-restart 60

	      Run the --ping-exit / --ping-restart timer only  if  we  have  a
	      remote  address.	Use this option	if you are starting the	daemon
	      in listen	mode (i.e. without an explicit --remote	peer), and you
	      don't  want  to start clocking timeouts until a remote peer con-

	      Don't close and reopen TUN/TAP device  or	 run  up/down  scripts
	      across SIGUSR1 or	--ping-restart restarts.

	      SIGUSR1  is a restart signal similar to SIGHUP, but which	offers
	      finer-grained control over reset options.

	      Don't re-read key	files across SIGUSR1 or	--ping-restart.

	      This option can be combined with --user nobody to	allow restarts
	      triggered	 by  the  SIGUSR1  signal.   Normally if you drop root
	      privileges in OpenVPN, the daemon	cannot be restarted  since  it
	      will now be unable to re-read protected key files.

	      This option solves the problem by	persisting keys	across SIGUSR1
	      resets, so they don't need to be re-read.

	      Preserve initially resolved local	IP  address  and  port	number
	      across SIGUSR1 or	--ping-restart restarts.

	      Preserve	most recently authenticated remote IP address and port
	      number across SIGUSR1 or --ping-restart restarts.

	      Disable paging by	calling	the POSIX mlockall function.  Requires
	      that OpenVPN be initially	run as root (though OpenVPN can	subse-
	      quently downgrade	its UID	using the --user option).

	      Using this option	ensures	that key material and tunnel data  are
	      never  written  to  disk due to virtual memory paging operations
	      which occur under	most modern  operating	systems.   It  ensures
	      that even	if an attacker was able	to crack the box running Open-
	      VPN, he would not	be able	 to  scan  the	system	swap  file  to
	      recover  previously  used	 ephemeral  keys, which	are used for a
	      period of	time governed by the --reneg options (see below), then
	      are discarded.

	      The  downside of using --mlock is	that it	will reduce the	amount
	      of physical memory available to other applications.

       --up cmd
	      Run command cmd after successful TUN/TAP device open (pre	--user
	      UID change).

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      The up command is	useful for  specifying	route  commands	 which
	      route IP traffic destined	for private subnets which exist	at the
	      other end	of the VPN connection into the tunnel.

	      For --dev	tun execute as:

	      cmd   tun_dev   tun_mtu	link_mtu   ifconfig_local_ip	ifcon-
	      fig_remote_ip [ init | restart ]

	      For --dev	tap execute as:

	      cmd  tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask
	      [	init | restart ]

	      See the "Environmental Variables"	section	below  for  additional
	      parameters passed	as environmental variables.

	      Note that	if cmd includes	arguments, all OpenVPN-generated argu-
	      ments will be appended to	them to	build an  argument  list  with
	      which the	executable will	be called.

	      Typically, cmd will run a	script to add routes to	the tunnel.

	      Normally	the  up	 script	 is called after the TUN/TAP device is
	      opened.  In this context,	the last command line parameter	passed
	      to  the script will be init.  If the --up-restart	option is also
	      used, the	up script will be called  for  restarts	 as  well.   A
	      restart  is considered to	be a partial reinitialization of Open-
	      VPN where	the TUN/TAP instance is	preserved  (the	 --persist-tun
	      option  will enable such preservation).  A restart can be	gener-
	      ated by a	SIGUSR1	signal,	a --ping-restart timeout, or a connec-
	      tion  reset  when	 the  TCP protocol is enabled with the --proto
	      option.  If a restart occurs, and	--up-restart has  been	speci-
	      fied,  the  up  script  will  be called with restart as the last

	      NOTE: on restart,	OpenVPN	will not pass the full set of environ-
	      ment  variables  to  the	script.	 Namely, everything related to
	      routing and gateways will	not be passed, as nothing needs	to  be
	      done  anyway - all the routing setup is already in place.	 Addi-
	      tionally,	the up-restart script will  run	 with  the  downgraded
	      UID/GID settings (if configured).

	      The  following  standalone example shows how the --up script can
	      be called	in both	an initialization and restart context.	(NOTE:
	      for security reasons, don't run the following example unless UDP
	      port 9999	is blocked by your firewall.  Also, the	 example  will
	      run indefinitely,	so you should abort with control-c).

	      openvpn  --dev  tun  --port 9999 --verb 4	--ping-restart 10 --up
	      'echo up'	--down 'echo down' --persist-tun --up-restart

	      Note that	OpenVPN	also provides the --ifconfig option  to	 auto-
	      matically	 ifconfig  the	TUN  device,  eliminating  the need to
	      define an	--up script, unless you	also want to configure	routes
	      in the --up script.

	      If  --ifconfig is	also specified,	OpenVPN	will pass the ifconfig
	      local and	remote endpoints on  the  command  line	 to  the  --up
	      script so	that they can be used to configure routes such as:

	      route add	-net netmask gw $5

	      Delay  TUN/TAP  open  and	 possible  --up	script execution until
	      after TCP/UDP connection establishment with peer.

	      In --proto udp mode, this	option normally	requires  the  use  of
	      --ping  to  allow	 connection  initiation	 to  be	 sensed	in the
	      absence of tunnel	data, since UDP	is a  "connectionless"	proto-

	      On  Windows,  this  option  will delay the TAP-Win32 media state
	      transitioning to	"connected"  until  connection	establishment,
	      i.e.  the	 receipt  of  the  first authenticated packet from the

       --down cmd
	      Run command cmd after TUN/TAP  device  close  (post  --user  UID
	      change  and/or --chroot ).  cmd consists of a path to script (or
	      executable program), optionally followed by arguments. The  path
	      and  arguments  may  be  single- or double-quoted	and/or escaped
	      using a backslash, and should be separated by one	or  more  spa-

	      Called  with  the	same parameters	and environmental variables as
	      the --up option above.

	      Note that	if  you	 reduce	 privileges  by	 using	--user	and/or
	      --group, your --down script will also run	at reduced privilege.

	      Call --down cmd/script before, rather than after,	TUN/TAP	close.

	      Enable  the --up and --down scripts to be	called for restarts as
	      well as initial program start.  This option  is  described  more
	      fully above in the --up option documentation.

       --setenv	name value
	      Set  a  custom  environmental  variable  name=value  to  pass to

       --setenv	FORWARD_COMPATIBLE 1
	      Relax config file	syntax checking	 so  that  unknown  directives
	      will  trigger a warning but not a	fatal error, on	the assumption
	      that a given unknown directive might be valid in future  OpenVPN

	      This option should be used with caution, as there	are good secu-
	      rity reasons for having OpenVPN fail if it detects problems in a
	      config  file.   Having  said  that,  there are valid reasons for
	      wanting new software features to gracefully degrade when encoun-
	      tered by older software versions.

	      It is also possible to tag a single directive so as not to trig-
	      ger a fatal error	if the	directive  isn't  recognized.	To  do
	      this, prepend the	following before the directive:	setenv opt

	      Versions	prior  to OpenVPN 2.3.3	will always ignore options set
	      with the setenv opt directive.

	      See also --ignore-unknown-option

       --setenv-safe name value
	      Set a custom environmental variable OPENVPN_name=value  to  pass
	      to script.

	      This  directive  is  designed  to	 be  pushed  by	 the server to
	      clients, and the prepending of "OPENVPN_"	to  the	 environmental
	      variable	is  a  safety precaution to prevent a LD_PRELOAD style
	      attack from a malicious or compromised server.

       --ignore-unknown-option opt1 opt2 opt3 ... optN
	      When one of options opt1 ... optN	is encountered in the configu-
	      ration file the configuration file parsing does not fail if this
	      OpenVPN  version	does  not   support   the   option.   Multiple
	      --ignore-unknown-option options can be given to support a	larger
	      number of	options	to ignore.

	      This option should be used with caution, as there	are good secu-
	      rity reasons for having OpenVPN fail if it detects problems in a
	      config file. Having said that, there are valid reasons for want-
	      ing new software features	to gracefully degrade when encountered
	      by older software	versions.

	      --ignore-unknown-option is available since OpenVPN 2.3.3.

       --script-security level
	      This directive offers policy-level control over OpenVPN's	 usage
	      of  external  programs and scripts.  Lower level values are more
	      restrictive, higher values are more  permissive.	 Settings  for

	      0	-- Strictly no calling of external programs.
	      1	 -- (Default) Only call	built-in executables such as ifconfig,
	      ip, route, or netsh.
	      2	-- Allow calling  of  built-in	executables  and  user-defined
	      3	 --  Allow passwords to	be passed to scripts via environmental
	      variables	(potentially unsafe).

	      OpenVPN releases before v2.3 also	supported a method flag	 which
	      indicated	how OpenVPN should call	external commands and scripts.
	      This could be either execve or system.  As of OpenVPN v2.3, this
	      flag  is	no  longer  accepted.	In  most *nix environments the
	      execve() approach	has been used without any issues.

	      Some directives such as --up allow options to be passed  to  the
	      external	script.	 In these cases	make sure the script name does
	      not contain any spaces or	the configuration  parser  will	 choke
	      because it can't determine where the script name ends and	script
	      options start.

	      To run scripts in	Windows	in earlier OpenVPN versions you	needed
	      to  either  add  a full path to the script interpreter which can
	      parse the	script or use the system flag to  run  these  scripts.
	      As  of  OpenVPN v2.3 it is now a strict requirement to have full
	      path to the  script  interpreter	when  running  non-executables
	      files.   This  is	not needed for executable files, such as .exe,
	      .com, .bat or .cmd files.	 For example, if  you  have  a	Visual
	      Basic script, you	must use this syntax now:

		  --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\	Files\\OpenVPN\\config\\my-up-script.vbs'

	      Please note the single quote marks and the escaping of the back-
	      slashes (\) and the space	character.

	      The reason the support for the system flag was removed is	due to
	      the  security  implications with shell expansions	when executing
	      scripts via the system() call.

	      Don't output a warning message  if  option  inconsistencies  are
	      detected	between	 peers.	 An example of an option inconsistency
	      would be where one peer uses --dev tun while the other peer uses
	      --dev tap.

	      Use  of  this option is discouraged, but is provided as a	tempo-
	      rary fix in situations where a recent version  of	 OpenVPN  must
	      connect to an old	version.

       --user user
	      Change the user ID of the	OpenVPN	process	to user	after initial-
	      ization, dropping	privileges in the  process.   This  option  is
	      useful  to  protect  the	system	in the event that some hostile
	      party was	able to	gain control of	an  OpenVPN  session.	Though
	      OpenVPN's	 security  features make this unlikely,	it is provided
	      as a second line of defense.

	      By setting user to nobody	or  somebody  similarly	 unprivileged,
	      the  hostile  party  would  be limited in	what damage they could
	      cause.  Of course	once you  take	away  privileges,  you	cannot
	      return  them  to	an  OpenVPN session.  This means, for example,
	      that if you want to reset	an OpenVPN daemon with a SIGUSR1  sig-
	      nal  (for	 example in response to	a DHCP reset), you should make
	      use of one or more of the	--persist options to ensure that Open-
	      VPN  doesn't  need to execute any	privileged operations in order
	      to restart (such as re-reading key files or running ifconfig  on
	      the TUN device).

       --group group
	      Similar  to  the --user option, this option changes the group ID
	      of the OpenVPN process to	group after initialization.

       --cd dir
	      Change directory to dir prior to reading any files such as  con-
	      figuration  files,  key  files,  scripts,	etc.  dir should be an
	      absolute path, with a leading "/", and without any references to
	      the current directory such as "."	or "..".

	      This  option  is useful when you are running OpenVPN in --daemon
	      mode, and	you want to consolidate	all of	your  OpenVPN  control
	      files in one location.

       --chroot	dir
	      Chroot  to dir after initialization.  --chroot essentially rede-
	      fines dir	as being the top level directory  tree	(/).   OpenVPN
	      will  therefore be unable	to access any files outside this tree.
	      This can be desirable from a security standpoint.

	      Since the	chroot operation is delayed  until  after  initializa-
	      tion,  most OpenVPN options that reference files will operate in
	      a	pre-chroot context.

	      In many cases, the dir parameter can point to  an	 empty	direc-
	      tory,  however complications can result when scripts or restarts
	      are executed after the chroot operation.

	      Note: The	SSL library will  probably  need  /dev/urandom	to  be
	      available	 inside	the chroot directory dir.  This	is because SSL
	      libraries	occasionally need  to  collect	fresh  random.	 Newer
	      linux  kernels  and  some	BSDs implement a getrandom() or	geten-
	      tropy() syscall that removes the need  for  /dev/urandom	to  be

       --setcon	context
	      Apply  SELinux  context  after  initialization. This essentially
	      provides the ability to restrict OpenVPN's rights	to  only  net-
	      work  I/O	 operations, thanks to SELinux.	This goes further than
	      --user and --chroot in that those	two, while being  great	 secu-
	      rity  features,  unfortunately  do not protect against privilege
	      escalation by exploitation of a vulnerable system	call. You  can
	      of  course  combine all three, but please	note that since	setcon
	      requires access to /proc you will	have to	provide	it inside  the
	      chroot directory (e.g. with mount	--bind).

	      Since  the  setcon  operation is delayed until after initializa-
	      tion, OpenVPN can	be restricted to just  network-related	system
	      calls,  whereas  by applying the context before startup (such as
	      the OpenVPN one provided in the SELinux Reference	Policies)  you
	      will  have to allow many things required only during initializa-

	      Like with	chroot,	 complications	can  result  when  scripts  or
	      restarts	are  executed after the	setcon operation, which	is why
	      you should really	consider using the  --persist-key  and	--per-
	      sist-tun options.

       --daemon	[progname]
	      Become  a	 daemon	 after	all  initialization functions are com-
	      pleted.  This option will	cause all message and error output  to
	      be  sent	to the syslog file (such as /var/log/messages),	except
	      for the output of	scripts	and ifconfig commands, which  will  go
	      to  /dev/null unless otherwise redirected.  The syslog redirect-
	      ion occurs immediately at	the point that --daemon	is  parsed  on
	      the  command  line  even	though	the daemonization point	occurs
	      later.  If  one  of  the	--log  options	is  present,  it  will
	      supercede	syslog redirection.

	      The optional progname parameter will cause OpenVPN to report its
	      program name to the system logger	as progname.  This can be use-
	      ful in linking OpenVPN messages in the syslog file with specific
	      tunnels.	When unspecified, progname defaults to "openvpn".

	      When OpenVPN is run with the --daemon option,  it	 will  try  to
	      delay  daemonization  until the majority of initialization func-
	      tions which are capable of generating fatal errors are complete.
	      This  means that initialization scripts can test the return sta-
	      tus of the openvpn command for a fairly reliable	indication  of
	      whether  the  command  has correctly initialized and entered the
	      packet forwarding	event loop.

	      In OpenVPN, the vast majority of errors which occur  after  ini-
	      tialization are non-fatal.

	      Note:  as	 soon  as  OpenVPN  has	daemonized, it can not ask for
	      usernames, passwords, or key pass	 phrases  anymore.   This  has
	      certain  consequences,  namely  that  using a password-protected
	      private key will fail unless the --askpass  option  is  used  to
	      tell OpenVPN to ask for the pass phrase (this requirement	is new
	      in 2.3.7,	and is a consequence of	calling	daemon()  before  ini-
	      tializing	the crypto layer).

	      Further,	using --daemon together	with --auth-user-pass (entered
	      on console) and --auth-nocache will fail as soon as key  renego-
	      tiation (and reauthentication) occurs.

       --syslog	[progname]
	      Direct  log output to system logger, but do not become a daemon.
	      See --daemon directive above for description of progname parame-

	      Output  errors  to stderr	instead	of stdout unless log output is
	      redirected by one	of the --log options.

	      Set the TOS field	of the tunnel packet to	what the payload's TOS

       --inetd [wait|nowait] [progname]
	      Use  this	 option	 when  OpenVPN	is being run from the inetd or
	      xinetd(8)	server.

	      The wait/nowait option must  match  what	is  specified  in  the
	      inetd/xinetd config file.	 The nowait mode can only be used with
	      --proto tcp-server.  The default is wait.	 The nowait  mode  can
	      be  used	to  instantiate	 the  OpenVPN  daemon as a classic TCP
	      server, where client connection requests are serviced on a  sin-
	      gle  port	 number.   For	additional information on this kind of
	      configuration,	see    the    OpenVPN	 FAQ:	  http://open-

	      This option precludes the	use of --daemon, --local, or --remote.
	      Note that	this option causes message and error output to be han-
	      dled in the same way as the --daemon option.  The	optional prog-
	      name parameter is	also handled exactly as	in --daemon.

	      Also note	that in	wait mode, each	OpenVPN	tunnel requires	a sep-
	      arate  TCP/UDP  port  and	a separate inetd or xinetd entry.  See
	      the OpenVPN 1.x HOWTO for	 an  example  on  using	 OpenVPN  with

       --log file
	      Output  logging  messages	 to  file,  including  output  to std-
	      out/stderr which	is  generated  by  called  scripts.   If  file
	      already  exists  it will be truncated.  This option takes	effect
	      immediately when it is parsed  in	 the  command  line  and  will
	      supercede	 syslog	 output	 if --daemon or	--inetd	is also	speci-
	      fied.  This option is persistent over the	entire	course	of  an
	      OpenVPN  instantiation and will not be reset by SIGHUP, SIGUSR1,
	      or --ping-restart.

	      Note that	on Windows, when OpenVPN is started as a service, log-
	      ging occurs by default without the need to specify this option.

       --log-append file
	      Append  logging  messages	 to  file.  If file does not exist, it
	      will be created.	This option behaves exactly like --log	except
	      that it appends to rather	than truncating	the log	file.

	      Avoid  writing timestamps	to log messages, even when they	other-
	      wise would be prepended. In particular, this applies to log mes-
	      sages sent to stdout.

       --writepid file
	      Write OpenVPN's main process ID to file.

       --nice n
	      Change  process priority after initialization ( n	greater	than 0
	      is lower priority, n less	than zero is higher priority).

	      (Experimental) Optimize TUN/TAP/UDP I/O  writes  by  avoiding  a
	      call  to	poll/epoll/select  prior  to the write operation.  The
	      purpose of such a	call would normally  be	 to  block  until  the
	      device or	socket is ready	to accept the write.  Such blocking is
	      unnecessary on some platforms which don't	support	write blocking
	      on UDP sockets or	TUN/TAP	devices.  In such cases, one can opti-
	      mize the event loop  by  avoiding	 the  poll/epoll/select	 call,
	      improving	CPU efficiency by 5% to	10%.

	      This  option  can	 only  be  used	 on  non-Windows systems, when
	      --proto udp is specified,	and when --shaper is NOT specified.

	      Configure	a multi-homed UDP server.  This	 option	 needs	to  be
	      used  when  a server has more than one IP	address	(e.g. multiple
	      interfaces, or secondary IP addresses), and is not using --local
	      to force binding to one specific address only.  This option will
	      add some extra lookups to	the packet path	to ensure that the UDP
	      reply  packets  are always sent from the address that the	client
	      is talking to. This is not supported on all  platforms,  and  it
	      adds more	processing, so it's not	enabled	by default.

	      Note: this option	is only	relevant for UDP servers.

	      Note  2:	if  you	 do  an	 IPv6+IPv4  dual-stack bind on a Linux
	      machine  with  multiple  IPv4  address,  connections   to	  IPv4
	      addresses	 will  not  work  right	on kernels before 3.15,	due to
	      missing kernel support for the IPv4-mapped case (some  distribu-
	      tions have ported	this to	earlier	kernel versions, though).

       --echo [parms...]
	      Echo parms to log	output.

	      Designed	to  be used to send messages to	a controlling applica-
	      tion which is receiving the OpenVPN log output.

       --remap-usr1 signal
	      Control whether internally or externally generated SIGUSR1  sig-
	      nals  are	 remapped to SIGHUP (restart without persisting	state)
	      or SIGTERM (exit).

	      signal can be set	to "SIGHUP"  or	 "SIGTERM".   By  default,  no
	      remapping	occurs.

       --verb n
	      Set  output  verbosity  to  n (default=1).  Each level shows all
	      info from	the previous levels.  Level 3 is  recommended  if  you
	      want a good summary of what's happening without being swamped by

	      0	-- No output except fatal errors.
	      1	to 4 --	Normal usage range.
	      5	-- Output R and	W characters to	the console  for  each	packet
	      read and write, uppercase	is used	for TCP/UDP packets and	lower-
	      case is used for TUN/TAP packets.
	      6	to 11 -- Debug	info  range  (see  errlevel.h  for  additional
	      information on debug levels).

       --status	file [n]
	      Write operational	status to file every n seconds.

	      Status  can  also	 be written to the syslog by sending a SIGUSR2

       --status-version	[n]
	      Choose the status	file format version number.  Currently	n  can
	      be 1, 2, or 3 and	defaults to 1.

       --mute n
	      Log  at  most n consecutive messages in the same category.  This
	      is useful	to limit repetitive logging of similar message types.

       --comp-lzo [mode]
	      Use fast LZO compression -- may add up to	1 byte per packet  for
	      incompressible  data.   mode  may	 be "yes", "no", or "adaptive"

	      In a server mode setup, it is possible to	selectively turn  com-
	      pression on or off for individual	clients.

	      First,  make  sure the client-side config	file enables selective
	      compression by having at least one --comp-lzo directive, such as
	      --comp-lzo  no.	This will turn off compression by default, but
	      allow a future directive push from  the  server  to  dynamically
	      change the on/off/adaptive setting.

	      Next in a	--client-config-dir file, specify the compression set-
	      ting for the client, for example:

		  comp-lzo yes
		  push "comp-lzo yes"

	      The first	line sets the comp-lzo setting for the server side  of
	      the link,	the second sets	the client side.

	      When  used in conjunction	with --comp-lzo, this option will dis-
	      able OpenVPN's adaptive compression algorithm.  Normally,	 adap-
	      tive compression is enabled with --comp-lzo.

	      Adaptive	compression  tries to optimize the case	where you have
	      compression enabled, but you are	sending	 predominantly	incom-
	      pressible	 (or  pre-compressed) packets over the tunnel, such as
	      an FTP or	rsync transfer of  a  large,  compressed  file.	  With
	      adaptive	compression, OpenVPN will periodically sample the com-
	      pression process to measure its efficiency.  If the  data	 being
	      sent  over  the  tunnel  is  already compressed, the compression
	      efficiency will be very low, triggering openvpn to disable  com-
	      pression for a period of time until the next re-sample test.

       --management IP port [pw-file]
	      Enable a TCP server on IP:port to	handle daemon management func-
	      tions.  pw-file, if specified, is	a password file	 (password  on
	      first line) or "stdin" to	prompt from standard input.  The pass-
	      word provided will set the password which	TCP clients will  need
	      to provide in order to access management functions.

	      The  management  interface  can  also  listen  on	 a unix	domain
	      socket, for those	platforms that support	it.   To  use  a  unix
	      domain  socket,  specify the unix	socket pathname	in place of IP
	      and set port to 'unix'.  While the default behavior is to	create
	      a	 unix  domain  socket that may be connected to by any process,
	      the   --management-client-user   and   --management-client-group
	      directives can be	used to	restrict access.

	      The  management  interface provides a special mode where the TCP
	      management link can operate over the tunnel itself.   To	enable
	      this  mode,  set IP = "tunnel".  Tunnel mode will	cause the man-
	      agement interface	to listen for a	TCP connection	on  the	 local
	      VPN address of the TUN/TAP interface.

	      While  the  management port is designed for programmatic control
	      of OpenVPN by other applications,	it is possible	to  telnet  to
	      the  port, using a telnet	client in "raw"	mode.  Once connected,
	      type "help" for a	list of	commands.

	      For detailed documentation on the	management interface, see  the
	      management-notes.txt  file in the	management folder of the Open-
	      VPN source distribution.

	      It is strongly recommended that IP be set	to  (local-
	      host)  to	 restrict  accessibility  of  the management server to
	      local clients.

	      Management interface will	connect	as a TCP/unix domain client to
	      IP:port  specified  by  --management rather than listen as a TCP
	      server or	on a unix domain socket.

	      If the client connection fails to	connect	or is disconnected,  a
	      SIGTERM signal will be generated causing OpenVPN to quit.

	      Query   management   channel   for   private  key	 password  and
	      --auth-user-pass username/password.  Only	query  the  management
	      channel for inputs which ordinarily would	have been queried from
	      the console.

	      Query management channel for proxy server	information for	a spe-
	      cific --remote (client-only).

	      Allow  management	 interface  to	override  --remote  directives
	      (client-only).   --management-external-key  Allows   usage   for
	      external private key file	instead	of --key option	(client-only).

	      Make  OpenVPN  forget  passwords when management session discon-

	      This directive does not affect the  --http-proxy	username/pass-
	      word.  It	is always cached.

	      Start OpenVPN in a hibernating state, until a client of the man-
	      agement interface	explicitly starts it  with  the	 hold  release

	      Send  SIGUSR1  signal  to	 OpenVPN if management session discon-
	      nects.  This is useful when you wish to  disconnect  an  OpenVPN
	      session  on  user	logoff.	For --management-client	this option is
	      not needed since a disconnect will always	generate a SIGTERM.

       --management-log-cache n
	      Cache the	most recent n lines of log file	history	for  usage  by
	      the management channel.

	      Report tunnel up/down events to management interface.

	      Gives  management	interface client the responsibility to authen-
	      ticate clients after their client	certificate has	been verified.
	      See  management-notes.txt	 in  OpenVPN distribution for detailed

	      Management interface clients must	specify	a packet  filter  file
	      for each connecting client.  See management-notes.txt in OpenVPN
	      distribution for detailed	notes.

       --management-client-user	u
	      When the management interface is	listening  on  a  unix	domain
	      socket, only allow connections from user u.

       --management-client-group g
	      When  the	 management  interface	is  listening on a unix	domain
	      socket, only allow connections from group	g.

       --plugin	module-pathname	[init-string]
	      Load plug-in module from the file	module-pathname, passing init-
	      string  as  an  argument	to the module initialization function.
	      Multiple plugin modules may be loaded into one OpenVPN process.

	      For more information and examples	on how to build	OpenVPN	 plug-
	      in  modules,  see	 the  README  file in the plugin folder	of the
	      OpenVPN source distribution.

	      If you are using an RPM install of OpenVPN, see /usr/share/open-
	      vpn/plugin.   The	 documentation is in doc and the actual	plugin
	      modules are in lib.

	      Multiple plugin modules can be cascaded, and modules can be used
	      in  tandem  with scripts.	 The modules will be called by OpenVPN
	      in the order that	they are declared in the config	file.  If both
	      a	 plugin	 and  script are configured for	the same callback, the
	      script will be called last.  If the  return  code	 of  the  mod-
	      ule/script controls an authentication function (such as tls-ver-
	      ify, auth-user-pass-verify, or client-connect), then every  mod-
	      ule  and script must return success (0) in order for the connec-
	      tion to be authenticated.

   Server Mode
       Starting	with OpenVPN 2.0, a multi-client TCP/UDP server	mode  is  sup-
       ported,	and  can  be enabled with the --mode server option.  In	server
       mode, OpenVPN will listen on a single port for incoming client  connec-
       tions.	All  client connections	will be	routed through a single	tun or
       tap interface.  This mode is designed for  scalability  and  should  be
       able  to	 support hundreds or even thousands of clients on sufficiently
       fast hardware.  SSL/TLS authentication must be used in this mode.

       --server	network	netmask	['nopool']
	      A	helper directive designed to  simplify	the  configuration  of
	      OpenVPN's	 server	 mode.	 This directive	will set up an OpenVPN
	      server which will	allocate addresses to clients out of the given
	      network/netmask.	 The  server itself will take the ".1" address
	      of the given network for use as the server-side endpoint of  the
	      local TUN/TAP interface.

	      For example, --server expands as follows:

		   mode	server
		   push	"topology [topology]"

		   if dev tun AND (topology == net30 OR	topology == p2p):
		     if	!nopool:
		     if	client-to-client:
		       push "route"
		     else if topology == net30:
		       push "route"

		   if dev tap OR (dev tun AND topology == subnet):
		     if	!nopool:
		     push "route-gateway"
		     if	route-gateway unset:

	      Don't   use   --server   if  you	are  ethernet  bridging.   Use
	      --server-bridge instead.

       --server-bridge gateway netmask pool-start-IP pool-end-IP

       --server-bridge ['nogw']

	      A	helper directive similar to --server which is designed to sim-
	      plify  the  configuration	 of  OpenVPN's server mode in ethernet
	      bridging configurations.

	      If --server-bridge is  used  without  any	 parameters,  it  will
	      enable  a	DHCP-proxy mode, where connecting OpenVPN clients will
	      receive an IP address for	their TAP adapter from the DHCP	server
	      running  on the OpenVPN server-side LAN.	Note that only clients
	      that support the binding of a DHCP client	with the  TAP  adapter
	      (such as Windows)	can support this mode.	The optional nogw flag
	      (advanced) indicates that	 gateway  information  should  not  be
	      pushed to	the client.

	      To  configure  ethernet  bridging,  you must first use your OS's
	      bridging capability to bridge the	TAP interface with the	ether-
	      net  NIC interface.  For example,	on Linux this is done with the
	      brctl tool, and with Windows XP it is done in the	 Network  Con-
	      nections	Panel  by  selecting the ethernet and TAP adapters and
	      right-clicking on	"Bridge	Connections".

	      Next you you must	manually set  the  IP/netmask  on  the	bridge
	      interface.     The    gateway    and   netmask   parameters   to
	      --server-bridge can be set  to  either  the  IP/netmask  of  the
	      bridge  interface,  or  the  IP/netmask  of  the	default	 gate-
	      way/router on the	bridged	subnet.

	      Finally, set aside a IP range in the bridged subnet, denoted  by
	      pool-start-IP  and  pool-end-IP, for OpenVPN to allocate to con-
	      necting clients.

	      For example,  server-bridge expands as follows:

		  mode server

		  push "route-gateway"

	      In another example, --server-bridge (without parameters) expands
	      as follows:

		  mode server

		  push "route-gateway dhcp"

	      Or --server-bridge nogw expands as follows:

		  mode server

       --push option
	      Push a config file option	back to	the client for	remote	execu-
	      tion.   Note that	option must be enclosed	in double quotes ("").
	      The client must specify --pull in	its config file.  The  set  of
	      options  which  can be pushed is limited by both feasibility and
	      security.	 Some  options	such  as  those	 which	would  execute
	      scripts are banned, since	they would effectively allow a compro-
	      mised server to execute arbitrary	code  on  the  client.	 Other
	      options  such  as	TLS or MTU parameters cannot be	pushed because
	      the client needs to know	them  before  the  connection  to  the
	      server can be initiated.

	      This is a	partial	list of	options	which can currently be pushed:
	      --route,	--route-gateway,  --route-delay,   --redirect-gateway,
	      --ip-win32,   --dhcp-option,  --inactive,	 --ping,  --ping-exit,
	      --ping-restart, --setenv,	--persist-key, --persist-tun,  --echo,
	      --comp-lzo, --socket-flags, --sndbuf, --rcvbuf

	      Don't  inherit  the  global  push	 list  for  a  specific	client
	      instance.	 Specify this option in	a client-specific context such
	      as  with	a --client-config-dir configuration file.  This	option
	      will ignore --push options at the	global config file level.

	      Push additional information about	the  client  to	 server.   The
	      additional information consists of the following data:

	      IV_VER=<version> -- the client OpenVPN version

	      IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]   --  the
	      client OS	platform

	      IV_HWADDR=<mac address> -- the MAC address  of  clients  default

	      IV_LZO_STUB=1 -- if client was built with	LZO stub capability

	      UV_<name>=<value>	 --  client  environment variables whose names
	      start with "UV_"

	      Disable a	particular client (based on the	common name) from con-
	      necting.	 Don't	use this option	to disable a client due	to key
	      or password compromise.  Use a CRL (certificate revocation list)
	      instead (see the --crl-verify option).

	      This  option must	be associated with a specific client instance,
	      which means that	it  must  be  specified	 either	 in  a	client
	      instance	config	file  using --client-config-dir	or dynamically
	      generated	using a	--client-connect script.

       --ifconfig-pool start-IP	end-IP [netmask]
	      Set aside	a pool of subnets to be	dynamically allocated to  con-
	      necting  clients,	 similar to a DHCP server.  For	tun-style tun-
	      nels, each client	will be	given a	/30 subnet (for	interoperabil-
	      ity  with	 Windows  clients).  For tap-style tunnels, individual
	      addresses	will be	allocated, and the optional netmask  parameter
	      will also	be pushed to clients.

       --ifconfig-pool-persist file [seconds]
	      Persist/unpersist	 ifconfig-pool data to file, at	seconds	inter-
	      vals (default=600), as well as on	program	startup	and shutdown.

	      The goal of this option is to provide  a	long-term  association
	      between  clients	(denoted by their common name) and the virtual
	      IP address assigned to them from the ifconfig-pool.  Maintaining
	      a	 long-term  association	 is good for clients because it	allows
	      them to effectively use the --persist-tun	option.

	      file is a	comma-delimited	 ASCII	file,  formatted  as  <Common-

	      If seconds = 0, file will	be treated as read-only.  This is use-
	      ful if you would like to treat file as a configuration file.

	      Note that	the entries in this file are  treated  by  OpenVPN  as
	      suggestions  only,  based	 on past associations between a	common
	      name and IP address.  They do not	guarantee that the given  com-
	      mon  name	will always receive the	given IP address.  If you want
	      guaranteed assignment, use --ifconfig-push

	      Modifies the --ifconfig-pool directive  to  allocate  individual
	      TUN  interface  addresses	 for  clients rather than /30 subnets.
	      NOTE:  This option is incompatible with Windows clients.

	      This option is deprecated, and should be replaced	with  --topol-
	      ogy p2p which is functionally equivalent.

       --ifconfig-push local remote-netmask [alias]
	      Push  virtual  IP	 endpoints  for	 client	tunnel,	overriding the
	      --ifconfig-pool dynamic allocation.

	      The parameters local and remote-netmask are set according	to the
	      --ifconfig  directive  which  you	 want to execute on the	client
	      machine to configure the remote end of the  tunnel.   Note  that
	      the parameters local and remote-netmask are from the perspective
	      of the client, not the server.  They may	be  DNS	 names	rather
	      than  IP	addresses,  in which case they will be resolved	on the
	      server at	the time of client connection.

	      The optional alias parameter may be  used	 in  cases  where  NAT
	      causes  the client view of its local endpoint to differ from the
	      server view.  In this case local/remote-netmask  will  refer  to
	      the  server  view	 while	alias/remote-netmask will refer	to the
	      client view.

	      This option must be associated with a specific client  instance,
	      which  means  that  it  must  be	specified  either  in a	client
	      instance config file using  --client-config-dir  or  dynamically
	      generated	using a	--client-connect script.

	      Remember also to include a --route directive in the main OpenVPN
	      config file which	encloses local,	so that	the kernel  will  know
	      to route it to the server's TUN/TAP interface.

	      OpenVPN's	 internal  client IP address selection algorithm works
	      as follows:

	      1	-- Use --client-connect	script generated file  for  static  IP
	      (first choice).
	      2	-- Use --client-config-dir file	for static IP (next choice).
	      3	 --  Use  --ifconfig-pool  allocation  for  dynamic  IP	 (last

       --iroute	network	[netmask]
	      Generate an internal route to a  specific	 client.  The  netmask
	      parameter, if omitted, defaults to

	      This  directive  can  be	used  to route a fixed subnet from the
	      server to	a particular client, regardless	of where the client is
	      connecting  from.	  Remember that	you must also add the route to
	      the system routing table as well (such as	by using  the  --route
	      directive).   The	 reason	 why two routes	are needed is that the
	      --route directive	routes the packet from the kernel to  OpenVPN.
	      Once  in	OpenVPN, the --iroute directive	routes to the specific

	      This option must be specified either in a	client instance	config
	      file  using --client-config-dir or dynamically generated using a
	      --client-connect script.

	      The --iroute directive also has an  important  interaction  with
	      --push "route ...".  --iroute essentially	defines	a subnet which
	      is owned by a particular client (we will call  this  client  A).
	      If  you would like other clients to be able to reach A's subnet,
	      you can use --push "route	..."  together with --client-to-client
	      to  effect  this.	  In  order for	all clients to see A's subnet,
	      OpenVPN must push	this route to all clients EXCEPT for A,	 since
	      the  subnet is already owned by A.  OpenVPN accomplishes this by
	      not not pushing a	route to a client if it	 matches  one  of  the
	      client's iroutes.

	      Because the OpenVPN server mode handles multiple clients through
	      a	single tun or tap interface, it	is effectively a router.   The
	      --client-to-client   flag	 tells	OpenVPN	 to  internally	 route
	      client-to-client traffic rather than pushing  all	 client-origi-
	      nating traffic to	the TUN/TAP interface.

	      When  this  option  is  used,  each  client will "see" the other
	      clients which are	currently connected.  Otherwise,  each	client
	      will  only see the server.  Don't	use this option	if you want to
	      firewall tunnel traffic using custom, per-client rules.

	      Allow multiple clients with the same common name to concurrently
	      connect.	In the absence of this option, OpenVPN will disconnect
	      a	client instance	upon connection	of a  new  client  having  the
	      same common name.

       --client-connect	cmd
	      Run command cmd on client	connection.

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      The command is passed the	common name  and  IP  address  of  the
	      just-authenticated  client as environmental variables (see envi-
	      ronmental	variable section below).  The command is  also	passed
	      the  pathname  of	 a  freshly created temporary file as the last
	      argument (after any arguments specified in cmd ),	to be used  by
	      the command to pass dynamically generated	config file directives
	      back to OpenVPN.

	      If the script wants to generate a	 dynamic  config  file	to  be
	      applied  on the server when the client connects, it should write
	      it to the	file named by the last argument.

	      See the --client-config-dir option below for options  which  can
	      be legally used in a dynamically generated config	file.

	      Note  that the return value of script is significant.  If	script
	      returns a	non-zero error status, it will cause the client	to  be

       --client-disconnect cmd
	      Like  --client-connect  but  called on client instance shutdown.
	      Will not be called unless	the --client-connect script and	 plug-
	      ins  (if	defined)  were previously called on this instance with
	      successful (0) status returns.

	      The exception to this rule is if the --client-disconnect command
	      or  plugins  are cascaded, and at	least one client-connect func-
	      tion succeeded, then ALL of the client-disconnect	functions  for
	      scripts  and  plugins  will  be called on	client instance	object
	      deletion,	even in	cases where some of the	related	client-connect
	      functions	returned an error status.

	      The  --client-disconnect	command	is passed the same pathname as
	      the corresponding	--client-connect command as its	last argument.
	      (after any arguments specified in	cmd ).

       --client-config-dir dir
	      Specify a	directory dir for custom client	config files.  After a
	      connecting client	has been authenticated,	OpenVPN	will  look  in
	      this  directory  for a file having the same name as the client's
	      X509 common name.	 If a matching file exists, it will be	opened
	      and  parsed  for	client-specific	 configuration options.	 If no
	      matching file is found, OpenVPN will instead  try	 to  open  and
	      parse a default file called "DEFAULT", which may be provided but
	      is not required. Note that the configuration files must be read-
	      able by the OpenVPN process after	it has dropped it's root priv-

	      This file	can specify a fixed IP	address	 for  a	 given	client
	      using  --ifconfig-push,  as  well	 as fixed subnets owned	by the
	      client using --iroute.

	      One of the useful	properties of this option is  that  it	allows
	      client  configuration  files to be conveniently created, edited,
	      or removed while the server is live, without needing to  restart
	      the server.

	      The  following  options  are legal in a client-specific context:
	      --push, --push-reset, --iroute, --ifconfig-push, and --config.

	      Require, as a condition of  authentication,  that	 a  connecting
	      client has a --client-config-dir file.

       --tmp-dir dir
	      Specify  a  directory  dir  for temporary	files.	This directory
	      will be used by openvpn processes	and script to communicate tem-
	      porary  data  with openvpn main process. Note that the directory
	      must be writable by the OpenVPN process  after  it  has  dropped
	      it's root	privileges.

	      This directory will be used by in	the following cases:

	      *	 --client-connect  scripts to dynamically generate client-spe-
	      cific configuration files.

	      *	OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY  plugin  hook  to	return
	      success/failure  via  auth_control_file when using deferred auth

	      *	OPENVPN_PLUGIN_ENABLE_PF plugin	hook to	pass  filtering	 rules
	      via pf_file

       --hash-size r v
	      Set the size of the real address hash table to r and the virtual
	      address table to v.  By default, both tables are	sized  at  256

       --bcast-buffers n
	      Allocate n buffers for broadcast datagrams (default=256).

       --tcp-queue-limit n
	      Maximum number of	output packets queued before TCP (default=64).

	      When OpenVPN is tunneling	data from a TUN/TAP device to a	remote
	      client over a TCP	connection, it is possible  that  the  TUN/TAP
	      device  might produce data at a faster rate than the TCP connec-
	      tion can support.	 When the  number  of  output  packets	queued
	      before  sending to the TCP socket	reaches	this limit for a given
	      client connection, OpenVPN will start to drop  outgoing  packets
	      directed at this client.

	      This  macro  sets	 the  TCP_NODELAY socket flag on the server as
	      well as pushes it	to connecting clients.	The  TCP_NODELAY  flag
	      disables	the  Nagle algorithm on	TCP sockets causing packets to
	      be transmitted immediately with low latency, rather than waiting
	      a	 short	period	of  time in order to aggregate several packets
	      into a larger containing packet.	In VPN applications over  TCP,
	      TCP_NODELAY is generally a good latency optimization.

	      The macro	expands	as follows:

		   if mode server:
		     socket-flags TCP_NODELAY
		     push "socket-flags	TCP_NODELAY"

       --max-clients n
	      Limit server to a	maximum	of n concurrent	clients.

       --max-routes-per-client n
	      Allow  a	maximum	of n internal routes per client	(default=256).
	      This is designed to help contain DoS attacks where an  authenti-
	      cated  client  floods  the server	with packets appearing to come
	      from many	unique MAC addresses, forcing the  server  to  deplete
	      virtual  memory  as  its	internal  routing table	expands.  This
	      directive	can be used in a --client-config-dir file or auto-gen-
	      erated by	a --client-connect script to override the global value
	      for a particular client.

	      Note that	this directive affects OpenVPN's internal routing  ta-
	      ble, not the kernel routing table.

       --stale-routes-check n [t]
	      Remove  routes haven't had activity for n	seconds	(i.e. the age-
	      ing time).

	      This check is ran	every t	seconds	(i.e. check interval).

	      If t is not present it defaults to n

	      This option helps	to keep	the dynamic routing table small.   See
	      also --max-routes-per-client

       --connect-freq n	sec
	      Allow  a	maximum	 of  n	new  connections  per sec seconds from
	      clients.	This is	designed to contain DoS	 attacks  which	 flood
	      the  server  with	 connection  requests using certificates which
	      will ultimately fail to authenticate.

	      This is an imperfect solution however, because  in  a  real  DoS
	      scenario,	legitimate connections might also be refused.

	      For  the best protection against DoS attacks in server mode, use
	      --proto udp and --tls-auth.

       --learn-address cmd
	      Run command cmd to validate client virtual addresses or routes.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      Three arguments will be appended to any arguments	in cmd as fol-

	      [1] operation -- "add", "update",	or "delete" based  on  whether
	      or  not the address is being added to, modified, or deleted from
	      OpenVPN's	internal routing table.
	      [2] address -- The address being learned or unlearned.  This can
	      be  an IPv4 address such as "", an IPv4 subnet such
	      as "", or an ethernet MAC address (when --dev tap
	      is being used) such as "00:FF:01:02:03:04".
	      [3] common name -- The common name on the	certificate associated
	      with the client linked to	this address.  Only present for	 "add"
	      or "update" operations, not "delete".

	      On  "add"	 or  "update" methods, if the script returns a failure
	      code (non-zero), OpenVPN will reject the address	and  will  not
	      modify its internal routing table.

	      Normally,	the cmd	script will use	the information	provided above
	      to set appropriate firewall entries on the  VPN  TUN/TAP	inter-
	      face.  Since OpenVPN provides the	association between virtual IP
	      or MAC address and the client's authenticated  common  name,  it
	      allows  a	user-defined script to configure firewall access poli-
	      cies with	regard to the client's high-level common name,	rather
	      than the low level client	virtual	addresses.

       --auth-user-pass-verify cmd method
	      Require  the  client to provide a	username/password (possibly in
	      addition to a client certificate)	for authentication.

	      OpenVPN will run command cmd to validate	the  username/password
	      provided by the client.

	      cmd  consists  of	 a  path  to  script  (or executable program),
	      optionally followed by arguments.	The path and arguments may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

	      If method	is set to "via-env", OpenVPN will call script with the
	      environmental  variables	username and password set to the user-
	      name/password strings provided by	the  client.   Be  aware  that
	      this  method  is insecure	on some	platforms which	make the envi-
	      ronment of a process publicly visible to other unprivileged pro-

	      If  method is set	to "via-file", OpenVPN will write the username
	      and password to the first	two lines of a	temporary  file.   The
	      filename	will  be passed	as an argument to script, and the file
	      will be  automatically  deleted  by  OpenVPN  after  the	script
	      returns.	 The  location	of the temporary file is controlled by
	      the --tmp-dir option, and	will default to	the current  directory
	      if  unspecified.	 For security, consider	setting	--tmp-dir to a
	      volatile storage medium such as /dev/shm (if available) to  pre-
	      vent the username/password file from touching the	hard drive.

	      The script should	examine	the username and password, returning a
	      success exit code	(0) if the client's authentication request  is
	      to be accepted, or a failure code	(1) to reject the client.

	      This  directive  is  designed to enable a	plugin-style interface
	      for extending OpenVPN's authentication capabilities.

	      To protect against a client passing a maliciously	 formed	 user-
	      name  or	password string, the username string must consist only
	      of these characters: alphanumeric, underbar ('_'),  dash	('-'),
	      dot  ('.'), or at	('@').	The password string can	consist	of any
	      printable	characters except for CR or LF.	 Any  illegal  charac-
	      ters in either the username or password string will be converted
	      to underbar ('_').

	      Care must	be taken by any	user-defined scripts to	avoid creating
	      a	 security vulnerability	in the way that	these strings are han-
	      dled.  Never use these strings in	such a way that	they might  be
	      escaped or evaluated by a	shell interpreter.

	      For  a  sample script that performs PAM authentication, see sam-
	      ple-scripts/ in the OpenVPN source distribution.

	      Clients that connect with	options	 that  are  incompatible  with
	      those of the server will be disconnected.

	      Options  that  will  be  compared	for compatibility include dev-
	      type, link-mtu, tun-mtu, proto,  tun-ipv6,  ifconfig,  comp-lzo,
	      fragment,	 keydir, cipher, auth, keysize,	secret,	no-replay, no-
	      iv, tls-auth, key-method,	tls-server, and	tls-client.

	      This option requires that	--disable-occ NOT be used.

	      Allow connections	 by  clients  that  do	not  specify  a	 user-
	      name/password.  Normally,	when --auth-user-pass-verify or	--man-
	      agement-client-auth is specified (or  an	authentication	plugin
	      module),	the  OpenVPN  server  daemon  will  require connecting
	      clients to specify a username and	password.  This	 option	 makes
	      the submission of	a username/password by clients optional, pass-
	      ing the responsibility to	the user-defined  authentication  mod-
	      ule/script  to  accept or	deny the client	based on other factors
	      (such as the setting of X509  certificate	 fields).   When  this
	      option  is used, and a connecting	client does not	submit a user-
	      name/password,  the  user-defined	 authentication	 module/script
	      will see the username and	password as being set to empty strings
	      ("").  The  authentication  module/script	 MUST  have  logic  to
	      detect this condition and	respond	accordingly.

	      Don't require client certificate,	client will authenticate using
	      username/password	only.  Be aware	that using this	 directive  is
	      less secure than requiring certificates from all clients.

	      If  you use this directive, the entire responsibility of authen-
	      tication will rest on your  --auth-user-pass-verify  script,  so
	      keep  in mind that bugs in your script could potentially compro-
	      mise the security	of your	VPN.

	      If you don't  use	 this  directive,  but	you  also  specify  an
	      --auth-user-pass-verify script, then OpenVPN will	perform	double
	      authentication.  The client  certificate	verification  AND  the
	      --auth-user-pass-verify script will need to succeed in order for
	      a	client to be authenticated and accepted	onto the VPN.

	      For --auth-user-pass-verify authentication,  use	the  authenti-
	      cated  username  as the common name, rather than the common name
	      from the client cert.

       --compat-names [no-remapping] (DEPRECATED)
	      Until OpenVPN v2.3 the format of the X.509  Subject  fields  was
	      formatted	like this:

	      /C=US/L=Somewhere/CN=John	Doe/

	      In  addition  the	old behaviour was to remap any character other
	      than alphanumeric, underscore ('_'), dash	('-'), dot ('.'),  and
	      slash  ('/')  to	underscore ('_').  The X.509 Subject string as
	      returned by the tls_id environmental variable,  could  addition-
	      ally contain colon (':') or equal	('=').

	      When  using  the	--compat-names option, this old	formatting and
	      remapping	will be	re-enabled again.  This	is purely  implemented
	      for  compatibility  reasons when using older plug-ins or scripts
	      which does not handle the	new formatting or UTF-8	characters.

	      In OpenVPN v2.3 the formatting of	these fields  changed  into  a
	      more standardised	format.	 It now	looks like:

	      C=US, L=Somewhere, CN=John Doe,

	      The  new	default	 format	 in  OpenVPN v2.3 also does not	do the
	      character	remapping which	happened  earlier.   This  new	format
	      enables  proper  support	for UTF-8 characters in	the usernames,
	      X.509 Subject fields and Common Name variables and  it  complies
	      to  the  RFC  2253, UTF-8	String Representation of Distinguished

	      The no-remapping mode flag can be	used with  the	--compat-names
	      option to	be compatible with the now deprecated --no-name-remap-
	      ping option.  It is only available at the	server.	When this mode
	      flag is used, the	Common Name, Subject, and username strings are
	      allowed to include any printable character including space,  but
	      excluding	control	characters such	as tab,	newline, and carriage-
	      return. no-remapping is only available on	the server side.

	      Please note: This	option is immediately deprecated.  It is  only
	      implemented  to  make  the transition to the new formatting less
	      intrusive.  It will be removed either in OpenVPN v2.4  or	 v2.5.
	      So  please  make	sure  you  use	the  --verify-x509-name	option
	      instead of --tls-remote as soon  as  possible  and  update  your
	      scripts where necessary.

       --no-name-remapping (DEPRECATED)
	      The   --no-name-remapping	  option   is	an  alias  for	--com-
	      pat-names	no-remapping.  It ensures  compatibility  with	server
	      configurations using the --no-name-remapping option.

	      Please  note: This option	is now deprecated.  It will be removed
	      either in	OpenVPN	v2.4 or	v2.5.  So please make sure you support
	      the  new X.509 name formatting described with the	--compat-names
	      option as	soon as	possible.

       --port-share host port [dir]
	      When run in TCP server mode, share the OpenVPN port with another
	      application,  such as an HTTPS server.  If OpenVPN senses	a con-
	      nection to its port which	is using a  non-OpenVPN	 protocol,  it
	      will proxy the connection	to the server at host:port.  Currently
	      only designed to work with HTTP/HTTPS, though it would be	 theo-
	      retically	possible to extend to other protocols such as ssh.

	      dir  specifies an	optional directory where a temporary file with
	      name N containing	content	C will be  dynamically	generated  for
	      each  proxy  connection,	where  N  is the source	IP:port	of the
	      client connection	and C is the source IP:port of the  connection
	      to  the proxy receiver.  This directory can be used as a dictio-
	      nary by the proxy	receiver to determine the origin of  the  con-
	      nection.	Each generated file will be automatically deleted when
	      the proxied connection is	torn down.

	      Not implemented on Windows.

   Client Mode
       Use client  mode	 when  connecting  to  an  OpenVPN  server  which  has
       --server, --server-bridge, or --mode server in it's configuration.

	      A	 helper	 directive  designed  to simplify the configuration of
	      OpenVPN's	client mode.  This directive is	equivalent to:


       --pull This option must be used on a client which is  connecting	 to  a
	      multi-client  server.   It  indicates  to	OpenVPN	that it	should
	      accept options pushed by the server, provided they are  part  of
	      the  legal  set of pushable options (note	that the --pull	option
	      is implied by --client ).

	      In particular, --pull allows the server to push  routes  to  the
	      client,  so  you should not use --pull or	--client in situations
	      where you	don't trust  the  server  to  have  control  over  the
	      client's routing table.

       --auth-user-pass	[up]
	      Authenticate  with server	using username/password.  up is	a file
	      containing username/password on 2	lines. If the password line is
	      missing, OpenVPN will prompt for one.

	      If  up  is  omitted, username/password will be prompted from the

	      The server configuration must specify an --auth-user-pass-verify
	      script to	verify the username/password provided by the client.

       --auth-retry type
	      Controls	how OpenVPN responds to	username/password verification
	      errors such as the client-side response to an  AUTH_FAILED  mes-
	      sage  from the server or verification failure of the private key

	      Normally used to prevent auth errors from	 being	fatal  on  the
	      client  side,  and to permit username/password requeries in case
	      of error.

	      An AUTH_FAILED message is	generated by the server	if the	client
	      fails  --auth-user-pass  authentication,	or  if the server-side
	      --client-connect script returns an error status when the	client
	      tries to connect.

	      type can be one of:

	      none  --	Client	will  exit  with  a  fatal  error (this	is the
	      nointeract -- Client will	retry the connection without  requery-
	      ing  for an --auth-user-pass username/password.  Use this	option
	      for unattended clients.
	      interact -- Client will requery for  an  --auth-user-pass	 user-
	      name/password  and/or  private  key password before attempting a

	      Note that	while this option cannot be pushed,  it	 can  be  con-
	      trolled from the management interface.

       --static-challenge t e
	      Enable  static  challenge/response protocol using	challenge text
	      t, with echo flag	given by e (0|1).

	      The echo flag indicates whether or not the  user's  response  to
	      the challenge should be echoed.

	      See  management-notes.txt	 in  the  OpenVPN  distribution	 for a
	      description of the OpenVPN challenge/response protocol.

       --server-poll-timeout n
	      when polling possible remote servers to connect to in  a	round-
	      robin  fashion,  spend  no  more	than  n	 seconds waiting for a
	      response before trying the next  server.	 As  this  only	 makes
	      sense in client-to-server	setups,	it cannot be used in point-to-
	      point setups using --secret symmetrical key mode.

       --explicit-exit-notify [n]
	      In UDP client mode or point-to-point mode, send  server/peer  an
	      exit  notification  if tunnel is restarted or OpenVPN process is
	      exited.  In client mode, on exit/restart,	this option will  tell
	      the  server  to  immediately  close  its	client instance	object
	      rather than waiting for a	timeout.  The n	parameter  (default=1)
	      controls the maximum number of attempts that the client will try
	      to resend	the exit notification message.	OpenVPN	will not  send
	      any exit notifications unless this option	is enabled.

   Data	Channel	Encryption Options:
       These options are meaningful for	both Static & TLS-negotiated key modes
       (must be	compatible between peers).

       --secret	file [direction]
	      Enable Static Key	encryption  mode  (non-TLS).   Use  pre-shared
	      secret file which	was generated with --genkey.

	      The  optional  direction parameter enables the use of 4 distinct
	      keys (HMAC-send, cipher-encrypt, HMAC-receive,  cipher-decrypt),
	      so that each data	flow direction has a different set of HMAC and
	      cipher keys.  This has a number of desirable security properties
	      including	 eliminating  certain  kinds of	DoS and	message	replay

	      When the direction parameter is omitted, 2 keys are  used	 bidi-
	      rectionally,  one	 for HMAC and the other	for encryption/decryp-

	      The direction parameter should always be complementary on	either
	      side  of	the  connection,  i.e. one side	should use "0" and the
	      other should use "1", or both sides should omit it altogether.

	      The direction parameter requires that file contains a  2048  bit
	      key.   While  pre-1.5  versions of OpenVPN generate 1024 bit key
	      files, any version  of  OpenVPN  which  supports	the  direction
	      parameter,  will also support 2048 bit key file generation using
	      the --genkey option.

	      Static key encryption mode has certain advantages,  the  primary
	      being ease of configuration.

	      There  are no certificates or certificate	authorities or compli-
	      cated negotiation	handshakes and protocols.  The	only  require-
	      ment  is	that  you have a pre-existing secure channel with your
	      peer (such as ssh	) to initially copy the	 key.	This  require-
	      ment, along with the fact	that your key never changes unless you
	      manually generate	a new one, makes it somewhat less secure  than
	      TLS mode (see below).  If	an attacker manages to steal your key,
	      everything that was ever encrypted with it is compromised.  Con-
	      trast  that  to the perfect forward secrecy features of TLS mode
	      (using Diffie Hellman key	exchange), where even if  an  attacker
	      was able to steal	your private key, he would gain	no information
	      to help him decrypt past sessions.

	      Another advantageous aspect of Static  Key  encryption  mode  is
	      that  it is a handshake-free protocol without any	distinguishing
	      signature	or feature (such as a  header  or  protocol  handshake
	      sequence)	that would mark	the ciphertext packets as being	gener-
	      ated by OpenVPN.	Anyone eavesdropping on	 the  wire  would  see
	      nothing but random-looking data.

	      Alternative  way	of specifying the optional direction parameter
	      for the --tls-auth  and  --secret	 options.  Useful  when	 using
	      inline files (See	section	on inline files).

       --auth alg
	      Authenticate  packets  with  HMAC	using message digest algorithm
	      alg.  (The default is SHA1 ).  HMAC is a commonly	 used  message
	      authentication algorithm (MAC) that uses a data string, a	secure
	      hash algorithm, and a key, to produce a digital signature.

	      OpenVPN's	usage of HMAC is to first encrypt a packet, then  HMAC
	      the resulting ciphertext.

	      In  static-key  encryption mode, the HMAC	key is included	in the
	      key file generated by --genkey.  In TLS mode, the	 HMAC  key  is
	      dynamically  generated and shared	between	peers via the TLS con-
	      trol channel.  If	OpenVPN	receives a packet with a bad  HMAC  it
	      will  drop  the  packet.	 HMAC  usually adds 16 or 20 bytes per
	      packet.  Set alg=none to disable authentication.

	      For	more	   information	     on	       HMAC	   see

       --cipher	alg
	      Encrypt  data  channel  packets  with cipher algorithm alg.  The
	      default is BF-CBC, an abbreviation for Blowfish in Cipher	 Block
	      Chaining	mode.  Blowfish	has the	advantages of being fast, very
	      secure, and allowing key sizes of	up to 448 bits.	  Blowfish  is
	      designed	to be used in situations where keys are	changed	infre-

	      For  more	 information  on  blowfish,  see   http://www.counter-

	      To  see  other  ciphers that are available with OpenVPN, use the
	      --show-ciphers option.

	      OpenVPN supports the CBC,	CFB, and OFB cipher modes, however CBC
	      is  recommended  and  CFB	 and OFB should	be considered advanced

	      Set alg=none to disable encryption.

       --keysize n
	      Size of cipher key in bits (optional).  If unspecified, defaults
	      to  cipher-specific  default.   The  --show-ciphers  option (see
	      below) shows all available OpenSSL ciphers,  their  default  key
	      sizes,  and  whether  the	 key size can be changed.  Use care in
	      changing a cipher's default key size.   Many  ciphers  have  not
	      been  extensively	 cryptanalyzed	with non-standard key lengths,
	      and a larger key may offer no real guarantee  of	greater	 secu-
	      rity, or may even	reduce security.

       --prng alg [nsl]
	      (Advanced) For PRNG (Pseudo-random number	generator), use	digest
	      algorithm	alg (default=sha1), and	set nsl	 (default=16)  to  the
	      size in bytes of the nonce secret	length (between	16 and 64).

	      Set  alg=none to disable the PRNG	and use	the OpenSSL RAND_bytes
	      function instead	for  all  of  OpenVPN's	 pseudo-random	number

       --engine	[engine-name]
	      Enable OpenSSL hardware-based crypto engine functionality.

	      If  engine-name is specified, use	a specific crypto engine.  Use
	      the --show-engines standalone option to list the crypto  engines
	      which are	supported by OpenSSL.

	      (Advanced)  Disable OpenVPN's protection against replay attacks.
	      Don't use	this option unless you are prepared to make a tradeoff
	      of greater efficiency in exchange	for less security.

	      OpenVPN provides datagram	replay protection by default.

	      Replay protection	is accomplished	by tagging each	outgoing data-
	      gram with	an identifier that is guaranteed to be unique for  the
	      key  being used.	The peer that receives the datagram will check
	      for the uniqueness of the	identifier.   If  the  identifier  was
	      already  received	 in a previous datagram, OpenVPN will drop the
	      packet.  Replay protection is important to defeat	 attacks  such
	      as  a  SYN flood attack, where the attacker listens in the wire,
	      intercepts a TCP SYN packet (identifying it by  the  context  in
	      which  it	 occurs	in relation to other packets), then floods the
	      receiving	peer with copies of this packet.

	      OpenVPN's	replay protection is implemented in slightly different
	      ways, depending on the key management mode you have selected.

	      In  Static  Key  mode  or	 when using an CFB or OFB mode cipher,
	      OpenVPN uses a 64	bit unique identifier  that  combines  a  time
	      stamp with an incrementing sequence number.

	      When  using  TLS	mode  for  key exchange	and a CBC cipher mode,
	      OpenVPN uses only	a 32 bit sequence number without a time	stamp,
	      since  OpenVPN  can  guarantee  the uniqueness of	this value for
	      each key.	 As in IPSec, if the sequence number is	close to wrap-
	      ping back	to zero, OpenVPN will trigger a	new key	exchange.

	      To  check	for replays, OpenVPN uses the sliding window algorithm
	      used by IPSec.

       --replay-window n [t]
	      Use a replay protection sliding-window of	size n and a time win-
	      dow of t seconds.

	      By default n is 64 (the IPSec default) and t is 15 seconds.

	      This  option  is	only  relevant	in UDP mode, i.e.  when	either
	      --proto udp is specifed, or no --proto option is specified.

	      When OpenVPN tunnels IP packets over UDP,	there is the possibil-
	      ity  that	 packets  might	 be dropped or delivered out of	order.
	      Because OpenVPN, like IPSec, is emulating	the  physical  network
	      layer,  it will accept an	out-of-order packet sequence, and will
	      deliver such packets in the same order they were received	to the
	      TCP/IP  protocol	stack,	provided  they	satisfy	 several  con-

	      (a) The packet cannot be a replay	(unless	--no-replay is	speci-
	      fied, which disables replay protection altogether).

	      (b)  If  a packet	arrives	out of order, it will only be accepted
	      if the difference	between	its sequence number  and  the  highest
	      sequence number received so far is less than n.

	      (c)  If  a packet	arrives	out of order, it will only be accepted
	      if it arrives no later than t seconds after any packet  contain-
	      ing a higher sequence number.

	      If  you  are using a network link	with a large pipeline (meaning
	      that the product of bandwidth and	latency	is high), you may want
	      to  use  a  larger  value	 for n.	 Satellite links in particular
	      often require this.

	      If you run OpenVPN  at  --verb  4,  you  will  see  the  message
	      "Replay-window  backtrack	 occurred  [x]"	every time the maximum
	      sequence number backtrack	seen thus far increases.  This can  be
	      used to calibrate	n.

	      There  is	some controversy on the	appropriate method of handling
	      packet reordering	at the security	layer.

	      Namely, to what extent should the	 security  layer  protect  the
	      encapsulated protocol from attacks which masquerade as the kinds
	      of normal	packet loss and	reordering that	 occur	over  IP  net-

	      The  IPSec  and  OpenVPN	approach is to allow packet reordering
	      within a certain fixed sequence number window.

	      OpenVPN adds to the IPSec	model by limiting the window  size  in
	      time as well as sequence space.

	      OpenVPN  also  adds  TCP	transport as an	option (not offered by
	      IPSec) in	which case OpenVPN can adopt a	very  strict  attitude
	      towards message deletion and reordering:	Don't allow it.	 Since
	      TCP guarantees reliability, any packet loss or reordering	 event
	      can be assumed to	be an attack.

	      In  this	sense, it could	be argued that TCP tunnel transport is
	      preferred	when tunneling non-IP  or  UDP	application  protocols
	      which  might  be	vulnerable to a	message	deletion or reordering
	      attack which falls within	the normal operational	parameters  of
	      IP networks.

	      So  I  would  make  the statement	that one should	never tunnel a
	      non-IP protocol or UDP application protocol  over	 UDP,  if  the
	      protocol might be	vulnerable to a	message	deletion or reordering
	      attack that falls	within the normal operating parameters of what
	      is  to  be  expected from	the physical IP	layer.	The problem is
	      easily fixed by simply using TCP as the VPN transport layer.

	      Silence the output of replay warnings, which are a common	 false
	      alarm  on	 WiFi networks.	 This option preserves the security of
	      the replay protection code without the verbosity associated with
	      warnings about duplicate packets.

       --replay-persist	file
	      Persist  replay-protection  state	 across	sessions using file to
	      save and reload the state.

	      This option will strengthen protection against  replay  attacks,
	      especially when you are using OpenVPN in a dynamic context (such
	      as with --inetd) when OpenVPN sessions  are  frequently  started
	      and stopped.

	      This  option will	keep a disk copy of the	current	replay protec-
	      tion state (i.e. the most	recent packet timestamp	 and  sequence
	      number  received	from  the  remote peer), so that if an OpenVPN
	      session is stopped and restarted,	it will	reject any replays  of
	      packets which were already received by the prior session.

	      This  option  only makes sense when replay protection is enabled
	      (the default) and	you are	using either  --secret	(shared-secret
	      key mode)	or TLS mode with --tls-auth.

	      (Advanced)  Disable  OpenVPN's  use of IV	(cipher	initialization
	      vector).	Don't use this option unless you are prepared to  make
	      a	tradeoff of greater efficiency in exchange for less security.

	      OpenVPN  uses  an	IV by default, and requires it for CFB and OFB
	      cipher modes (which are totally insecure without it).  Using  an
	      IV  is  important	 for security when multiple messages are being
	      encrypted/decrypted with the same	key.

	      IV is implemented	differently depending on the cipher mode used.

	      In CBC mode, OpenVPN uses	a pseudo-random	IV for each packet.

	      In CFB/OFB mode, OpenVPN uses a unique sequence number and  time
	      stamp as the IV.	In fact, in CFB/OFB mode, OpenVPN uses a data-
	      gram space-saving	optimization that uses the  unique  identifier
	      for datagram replay protection as	the IV.

	      Enable prediction	resistance on PolarSSL's RNG.

	      Enabling	prediction resistance causes the RNG to	reseed in each
	      call for random. Reseeding this often can	 quickly  deplete  the
	      kernel entropy pool.

	      If  you  need this option, please	consider running a daemon that
	      adds entropy to the kernel pool.

	      Note that	this option only works with PolarSSL versions  greater
	      than 1.1.

	      Do  a  self-test	of  OpenVPN's crypto options by	encrypting and
	      decrypting  test	packets	 using	the  data  channel  encryption
	      options specified	above.	This option does not require a peer to
	      function,	and  therefore	can  be	 specified  without  --dev  or

	      The typical usage	of --test-crypto would be something like this:

	      openvpn --test-crypto --secret key


	      openvpn --test-crypto --secret key --verb	9

	      This  option  is	very  useful to	test OpenVPN after it has been
	      ported to	a new platform,	or to isolate  problems	 in  the  com-
	      piler,  OpenSSL crypto library, or OpenVPN's crypto code.	 Since
	      it is a self-test	mode, problems with encryption and authentica-
	      tion can be debugged independently of network and	tunnel issues.

   TLS Mode Options:
       TLS  mode  is the most powerful crypto mode of OpenVPN in both security
       and flexibility.	 TLS mode works	by establishing	control	and data chan-
       nels  which are multiplexed over	a single TCP/UDP port.	OpenVPN	initi-
       ates a TLS session over the control channel and	uses  it  to  exchange
       cipher  and  HMAC  keys	to  protect the	data channel.  TLS mode	uses a
       robust reliability layer	over the UDP connection	for all	control	 chan-
       nel  communication, while the data channel, over	which encrypted	tunnel
       data passes, is forwarded without any mediation.	  The  result  is  the
       best  of	 both  worlds: a fast data channel that	forwards over UDP with
       only the	overhead of encrypt, decrypt, and HMAC functions, and  a  con-
       trol channel that provides all of the security features of TLS, includ-
       ing  certificate-based  authentication  and  Diffie   Hellman   forward

       To  use TLS mode, each peer that	runs OpenVPN should have its own local
       certificate/key pair ( --cert and --key ), signed by the	root  certifi-
       cate which is specified in --ca.

       When  two OpenVPN peers connect,	each presents its local	certificate to
       the other.  Each	peer will then check that its partner peer presented a
       certificate  which  was signed by the master root certificate as	speci-
       fied in --ca.

       If that check on	both peers succeeds, then  the	TLS  negotiation  will
       succeed,	 both  OpenVPN peers will exchange temporary session keys, and
       the tunnel will begin passing data.

       The OpenVPN distribution	contains a set of  scripts  for	 managing  RSA
       certificates & keys, located in the easy-rsa subdirectory.

       The  easy-rsa  package  is also rendered	in web form here: http://open-

	      Enable TLS and assume server role	during	TLS  handshake.	  Note
	      that  OpenVPN  is	 designed  as a	peer-to-peer application.  The
	      designation of client or server is only for the purpose of nego-
	      tiating the TLS control channel.

	      Enable TLS and assume client role	during TLS handshake.

       --ca file
	      Certificate authority (CA) file in .pem format, also referred to
	      as the root certificate.	This file can have  multiple  certifi-
	      cates  in	.pem format, concatenated together.  You can construct
	      your own certificate authority certificate and  private  key  by
	      using a command such as:

	      openssl req -nodes -new -x509 -keyout ca.key -out	ca.crt

	      Then  edit  your openssl.cnf file	and edit the certificate vari-
	      able to point to your new	root certificate ca.crt.

	      For testing purposes only, the OpenVPN distribution  includes  a
	      sample  CA certificate (ca.crt).	Of course you should never use
	      the test certificates and	test keys distributed with OpenVPN  in
	      a	 production environment, since by virtue of the	fact that they
	      are distributed with OpenVPN, they are totally insecure.

       --capath	dir
	      Directory	 containing  trusted  certificates  (CAs  and	CRLs).
	      Available	with OpenSSL version >=	0.9.7 dev.  Not	available with

	      When using the --capath option, you are required to supply valid
	      CRLs  for	the CAs	too.  CAs in the capath	directory are expected
	      to  be  named  <hash>.<n>.   CRLs	 are  expected	to  be	 named
	      <hash>.r<n>.  See	the -CApath option of openssl verify , and the
	      -hash option of openssl x509 and openssl crl for	more  informa-

       --dh file
	      File   containing	 Diffie	 Hellman  parameters  in  .pem	format
	      (required	for --tls-server only).	Use

	      openssl dhparam -out dh1024.pem 1024

	      to generate your	own,  or  use  the  existing  dh1024.pem  file
	      included	with the OpenVPN distribution.	Diffie Hellman parame-
	      ters may be considered public.

       --cert file
	      Local peer's signed certificate in .pem format --	must be	signed
	      by  a  certificate  authority whose certificate is in --ca file.
	      Each peer	in an OpenVPN link running in TLS mode should have its
	      own  certificate	and  private key file.	In addition, each cer-
	      tificate should have been	signed by the  key  of	a  certificate
	      authority	 whose	public	key  resides  in  the --ca certificate
	      authority	file.	You  can  easily  make	your  own  certificate
	      authority	 (see  above) or pay money to use a commercial service
	      such as (in which case	you will be helping to finance
	      the world's second space tourist :).  To generate	a certificate,
	      you can use a command such as:

	      openssl req -nodes -new -keyout mycert.key -out mycert.csr

	      If your certificate  authority  private  key  lives  on  another
	      machine,	copy  the  certificate signing request (mycert.csr) to
	      this other machine (this can be done over	 an  insecure  channel
	      such  as	email).	  Now sign the certificate with	a command such

	      openssl ca -out mycert.crt -in mycert.csr

	      Now copy the certificate (mycert.crt) back  to  the  peer	 which
	      initially	 generated  the	 .csr  file (this can be over a	public
	      medium).	Note that the openssl ca command reads the location of
	      the  certificate	authority key from its configuration file such
	      as /usr/share/ssl/openssl.cnf -- note also that for  certificate
	      authority	functions, you must set	up the files index.txt (may be
	      empty) and serial	(initialize to 01 ).

       --extra-certs file
	      Specify a	file containing	one or more  PEM  certs	 (concatenated
	      together)	that complete the local	certificate chain.

	      This  option  is useful for "split" CAs, where the CA for	server
	      certs is different than the CA for client	certs.	Putting	 certs
	      in  this	file allows them to be used to complete	the local cer-
	      tificate chain without trusting them to verify the  peer-submit-
	      ted  certificate,	 as would be the case if the certs were	placed
	      in the ca	file.

       --key file
	      Local peer's private key in .pem format.	Use  the  private  key
	      which  was generated when	you built your peer's certificate (see
	      --cert file above).

       --tls-version-min version ['or-highest']
	      Enable TLS version negotiation, and set the minimum TLS  version
	      we  will	accept from the	peer (default is "1.0").  Examples for
	      version include "1.0", "1.1",  or	 "1.2".	  If  'or-highest'  is
	      specified	and version is not recognized, we will only accept the
	      highest TLS version supported by the local SSL implementation.

	      Also see --tls-version-max below,	for information	on compatibil-

       --tls-version-max version
	      Set  the maximum TLS version we will use (default	is the highest
	      version supported).  Examples for	version	include	"1.0",	"1.1",
	      or "1.2".

	      If  and  only  if	 this  is set to 1.0, and OpenSSL is used (not
	      PolarSSL), then OpenVPN will set up OpenSSL to use a fixed TLSv1
	      handshake.  All  other  configurations will autonegotiate	in the
	      given limits, and	the choice of handshake	versions  is  left  to
	      the SSL implementation.

       --pkcs12	file
	      Specify a	PKCS #12 file containing local private key, local cer-
	      tificate,	and root CA certificate.   This	 option	 can  be  used
	      instead	of  --ca,  --cert,  and	 --key.	  Not  available  with

       --verify-hash hash
	      Specify SHA1 fingerprint for level-1 cert.  The level-1 cert  is
	      the  CA  (or intermediate	cert) that signs the leaf certificate,
	      and is one removed from the leaf certificate in the direction of
	      the  root.  When accepting a connection from a peer, the level-1
	      cert fingerprint must match  hash	 or  certificate  verification
	      will  fail.   Hash  is  specified	 as  XX:XX:...	 For  example:

       --pkcs11-cert-private [0|1]...
	      Set if access to certificate object should  be  performed	 after
	      login.  Every provider has its own setting.

       --pkcs11-id name
	      Specify  the serialized certificate id to	be used. The id	can be
	      gotten by	the standalone --show-pkcs11-ids option.

	      Acquire PKCS#11 id from management interface.  In	 this  case  a
	      NEED-STR	'pkcs11-id-request'  real-time	message	 will be trig-
	      gered, application may use pkcs11-id-count command  to  retrieve
	      available	 number	 of certificates, and pkcs11-id-get command to
	      retrieve certificate id and certificate body.

       --pkcs11-pin-cache seconds
	      Specify how many seconds the PIN can be cached, the  default  is
	      until the	token is removed.

       --pkcs11-protected-authentication [0|1]...
	      Use  PKCS#11 protected authentication path, useful for biometric
	      and external keypad devices.  Every provider has	its  own  set-

       --pkcs11-providers provider...
	      Specify  a RSA Security Inc. PKCS	#11 Cryptographic Token	Inter-
	      face (Cryptoki) providers	to load.   This	 option	 can  be  used
	      instead of --cert, --key,	and --pkcs12.

	      If p11-kit is present on the system, its	module
	      will  be	loaded	by  default  if	 either	 the  --pkcs11-id   or
	      --pkcs11-id-management	options	   are	  specified    without
	      --pkcs11-provider	being given.

       --pkcs11-private-mode mode...
	      Specify which method to use in  order  to	 perform  private  key
	      operations.    A	different  mode	 can  be  specified  for  each
	      provider.	 Mode is encoded as hex	number,	and can	be a mask  one
	      of the following:

	      0	(default) -- Try to determine automatically.
	      1	-- Use sign.
	      2	-- Use sign recover.
	      4	-- Use decrypt.
	      8	-- Use unwrap.

       --cryptoapicert select-string
	      Load  the	 certificate and private key from the Windows Certifi-
	      cate System Store	(Windows/OpenSSL Only).

	      Use this option instead of --cert	and --key.

	      This makes it possible to	use any	smart card, supported by  Win-
	      dows,  but  also	any  kind of certificate, residing in the Cert
	      Store, where you have access to the private  key.	  This	option
	      has been tested with a couple of different smart cards (GemSAFE,
	      Cryptoflex, and Swedish Post Office eID) on the client side, and
	      also an imported PKCS12 software certificate on the server side.

	      To select	a certificate, based on	a substring search in the cer-
	      tificate's subject:

	      cryptoapicert "SUBJ:Peter	Runestig"

	      To select	a certificate, based on	certificate's thumbprint:

	      cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."

	      The thumbprint hex string	can easily be copy-and-pasted from the
	      Windows Certificate Store	GUI.

       --key-method m
	      Use  data	channel	key negotiation	method m.  The key method must
	      match on both sides of the connection.

	      After OpenVPN negotiates a TLS session, a	new set	 of  keys  for
	      protecting  the  tunnel  data channel is generated and exchanged
	      over the TLS session.

	      In method	1 (the default for OpenVPN 1.x), both  sides  generate
	      random  encrypt  and  HMAC-send  keys which are forwarded	to the
	      other host over the TLS channel.

	      In method	2, (the	default	for OpenVPN 2.0) the client  generates
	      a	 random	key.  Both client and server also generate some	random
	      seed material.  All key source material is  exchanged  over  the
	      TLS  channel.  The  actual  keys are generated using the TLS PRF
	      function,	taking source entropy from  both  client  and  server.
	      Method  2	 is  designed  to  closely parallel the	key generation
	      process used by TLS 1.0.

	      Note that	in TLS mode, two separate levels of keying occur:

	      (1) The TLS connection is	initially negotiated, with both	 sides
	      of  the connection producing certificates	and verifying the cer-
	      tificate (or other authentication	info provided)	of  the	 other
	      side.  The --key-method parameter	has no effect on this process.

	      (2)  After the TLS connection is established, the	tunnel session
	      keys are separately negotiated  over  the	 existing  secure  TLS
	      channel.	 Here,	--key-method  determines the derivation	of the
	      tunnel session keys.

       --tls-cipher l
	      A	list l of allowable TLS	ciphers	delimited by a colon (":").

	      This setting can be used to ensure that  certain	cipher	suites
	      are used (or not used) for the TLS connection.  OpenVPN uses TLS
	      to secure	the control channel, over which	the keys that are used
	      to protect the actual VPN	traffic	are exchanged.

	      The  supplied  list  of ciphers is (after	potential OpenSSL/IANA
	      name translation)	simply supplied	to the crypto library.	Please
	      see the OpenSSL and/or PolarSSL documentation for	details	on the
	      cipher list interpretation.

	      Use --show-tls to	see a list of TLS ciphers  supported  by  your
	      crypto library.

	      Warning!	 --tls-cipher  is  an  expert feature, which - if used
	      correcly - can improve the security of your VPN connection.  But
	      it  is  also easy	to unwittingly use it to carefully align a gun
	      with your	foot, or just break your connection.  Use with care!

	      The default for --tls-cipher is to use PolarSSL's	default	cipher
	      list	     when	   using	  PolarSSL	    or
	      "DEFAULT:!EXP:!LOW:!MEDIUM:!PSK:!SRP:!kRSA" when using OpenSSL.

       --tls-timeout n
	      Packet retransmit	timeout	on TLS control channel if no  acknowl-
	      edgment  from remote within n seconds (default=2).  When OpenVPN
	      sends a control packet to	its peer, it will expect to receive an
	      acknowledgement  within  n  seconds  or  it  will	retransmit the
	      packet, subject to a  TCP-like  exponential  backoff  algorithm.
	      This  parameter  only  applies to	control	channel	packets.  Data
	      channel packets (which carry encrypted tunnel  data)  are	 never
	      acknowledged, sequenced, or retransmitted	by OpenVPN because the
	      higher level network protocols running on	top of the tunnel such
	      as TCP expect this role to be left to them.

       --reneg-bytes n
	      Renegotiate  data	 channel  key  after  n	bytes sent or received
	      (disabled	by default).  OpenVPN allows the lifetime of a key  to
	      be  expressed as a number	of bytes encrypted/decrypted, a	number
	      of packets, or a number of seconds.  A key renegotiation will be
	      forced if	any of these three criteria are	met by either peer.

       --reneg-pkts n
	      Renegotiate  data	 channel key after n packets sent and received
	      (disabled	by default).

       --reneg-sec n
	      Renegotiate data channel key after n seconds (default=3600).

	      When using dual-factor authentication, note  that	 this  default
	      value  may  cause	 the  end user to be challenged	to reauthorize
	      once per hour.

	      Also, keep in mind that this option can  be  used	 on  both  the
	      client  and  server,  and	whichever uses the lower value will be
	      the one to trigger the renegotiation.  A common  mistake	is  to
	      set  --reneg-sec	to  a  higher  value  on  either the client or
	      server, while the	other side of the connection  is  still	 using
	      the  default  value of 3600 seconds, meaning that	the renegotia-
	      tion will	still occur once per 3600 seconds.  The	solution is to
	      increase --reneg-sec on both the client and server, or set it to
	      0	on one side of the connection (to disable), and	to your	chosen
	      value on the other side.

       --hand-window n
	      Handshake	 Window	 --  the  TLS-based key	exchange must finalize
	      within n seconds of handshake initiation by any peer (default  =
	      60  seconds).   If  the handshake	fails we will attempt to reset
	      our connection with our peer and try again.  Even	in  the	 event
	      of  handshake  failure we	will still use our expiring key	for up
	      to --tran-window seconds to maintain continuity of  transmission
	      of tunnel	data.

       --tran-window n
	      Transition  window  --  our  old	key can	live this many seconds
	      after a new a key	renegotiation begins (default =	3600 seconds).
	      This  feature  allows  for a graceful transition from old	to new
	      key, and removes the key renegotiation sequence from the	criti-
	      cal path of tunnel data forwarding.

	      After  initially	connecting  to a remote	peer, disallow any new
	      connections.  Using this option means that a remote peer	cannot
	      connect, disconnect, and then reconnect.

	      If  the  daemon  is reset	by a signal or --ping-restart, it will
	      allow one	new connection.

	      --single-session can be used with	--ping-exit or	--inactive  to
	      create a single dynamic session that will	exit when finished.

	      Exit on TLS negotiation failure.

       --tls-auth file [direction]
	      Add an additional	layer of HMAC authentication on	top of the TLS
	      control channel to protect against DoS attacks.

	      In a nutshell, --tls-auth	enables	a kind of "HMAC	 firewall"  on
	      OpenVPN's	 TCP/UDP port, where TLS control channel packets bear-
	      ing an incorrect HMAC signature can be dropped immediately with-
	      out response.

	      file  (required)	is  a key file which can be in one of two for-

	      (1) An OpenVPN static key	file generated by  --genkey  (required
	      if direction parameter is	used).

	      (2)  DEPRECATED  A  freeform  passphrase file.  In this case the
	      HMAC key will be derived by taking a secure hash of  this	 file,
	      similar  to the md5sum(1)	or sha1sum(1) commands.	This option is
	      deprecated and will  stop	 working  in  OpenVPN  2.4  and	 newer

	      OpenVPN  will  first  try	 format	 (1), and if the file fails to
	      parse as a static	key file, format (2) will be used.

	      See the --secret option for more	information  on	 the  optional
	      direction	parameter.

	      --tls-auth is recommended	when you are running OpenVPN in	a mode
	      where it is listening for	packets	from any IP address,  such  as
	      when  --remote  is  not specified, or --remote is	specified with

	      The rationale for	this feature is	as follows.   TLS  requires  a
	      multi-packet  exchange before it is able to authenticate a peer.
	      During this time before authentication,  OpenVPN	is  allocating
	      resources	 (memory  and CPU) to this potential peer.  The	poten-
	      tial peer	is also	exposing many parts of OpenVPN and the OpenSSL
	      library  to  the packets it is sending.  Most successful network
	      attacks today seek to either exploit bugs	in programs  (such  as
	      buffer  overflow	attacks) or force a program to consume so many
	      resources	that it	becomes	unusable.  Of course the first line of
	      defense  is always to produce clean, well-audited	code.  OpenVPN
	      has been written with buffer overflow attack prevention as a top
	      priority.	  But  as  history  has	shown, many of the most	widely
	      used network applications	have, from time	 to  time,  fallen  to
	      buffer overflow attacks.

	      So  as  a	 second	 line  of defense, OpenVPN offers this special
	      layer of authentication on top of	the  TLS  control  channel  so
	      that  every packet on the	control	channel	is authenticated by an
	      HMAC signature and a unique ID for replay	protection.  This sig-
	      nature  will  also  help protect against DoS (Denial of Service)
	      attacks.	An important rule of thumb in  reducing	 vulnerability
	      to  DoS  attacks is to minimize the amount of resources a	poten-
	      tial, but	as yet unauthenticated,	client is able to consume.

	      --tls-auth does this by signing every TLS	control	channel	packet
	      with  an HMAC signature, including packets which are sent	before
	      the TLS level has	had a chance to	authenticate  the  peer.   The
	      result  is  that	packets	 without  the correct signature	can be
	      dropped immediately upon reception, before they have a chance to
	      consume  additional system resources such	as by initiating a TLS
	      handshake.   --tls-auth  can  be	strengthened  by  adding   the
	      --replay-persist option which will keep OpenVPN's	replay protec-
	      tion state in a file so that it is not lost across restarts.

	      It should	be emphasized that this	feature	is optional  and  that
	      the  passphrase/key file used with --tls-auth gives a peer noth-
	      ing more than the	power to initiate a TLS	handshake.  It is  not
	      used to encrypt or authenticate any tunnel data.

       --askpass [file]
	      Get  certificate	password from console or file before we	daemo-

	      For the extremely	security conscious, it is possible to  protect
	      your  private  key  with	a password.  Of	course this means that
	      every time the OpenVPN daemon is started you must	 be  there  to
	      type  the	 password.   The  --askpass option allows you to start
	      OpenVPN from the command line.  It will query you	for a password
	      before  it daemonizes.  To protect a private key with a password
	      you should omit the -nodes option	when you use the openssl  com-
	      mand line	tool to	manage certificates and	private	keys.

	      If  file	is specified, read the password	from the first line of
	      file.  Keep in mind that storing your password in	a  file	 to  a
	      certain  extent invalidates the extra security provided by using
	      an encrypted key.

	      Don't cache --askpass or --auth-user-pass	username/passwords  in
	      virtual memory.

	      If  specified,  this directive will cause	OpenVPN	to immediately
	      forget username/password inputs  after  they  are	 used.	 As  a
	      result,  when  OpenVPN needs a username/password,	it will	prompt
	      for input	from stdin, which may be  multiple  times  during  the
	      duration of an OpenVPN session.

	      When  using  --auth-nocache  in combination with a user/password
	      file and --chroot	or --daemon, make  sure	 to  use  an  absolute

	      This  directive  does not	affect the --http-proxy	username/pass-
	      word.  It	is always cached.

       --tls-verify cmd
	      Run command cmd to verify	the X509 name of a pending TLS connec-
	      tion  that has otherwise passed all other	tests of certification
	      (except for revocation via --crl-verify directive;  the  revoca-
	      tion test	occurs after the --tls-verify test).

	      cmd  should return 0 to allow the	TLS handshake to proceed, or 1
	      to fail.

	      cmd consists of  a  path	to  script  (or	 executable  program),
	      optionally  followed by arguments. The path and arguments	may be
	      single- or double-quoted and/or escaped using a  backslash,  and
	      should be	separated by one or more spaces.

	      When  cmd	is executed two	arguments are appended after any argu-
	      ments specified in cmd , as follows:

	      cmd certificate_depth subject

	      These arguments are, respectively, the current certificate depth
	      and the X509 common name (cn) of the peer.

	      This  feature is useful if the peer you want to trust has	a cer-
	      tificate which was signed	by a certificate  authority  who  also
	      signed many other	certificates, where you	don't necessarily want
	      to trust all of them, but	rather be selective about  which  peer
	      certificate you will accept.  This feature allows	you to write a
	      script which will	test the X509 name on a	certificate and	decide
	      whether  or not it should	be accepted.  For a simple perl	script
	      which will test the common name field on	the  certificate,  see
	      the file verify-cn in the	OpenVPN	distribution.

	      See  the	"Environmental Variables" section below	for additional
	      parameters passed	as environmental variables.

       --tls-export-cert directory
	      Store the	certificates the clients uses upon connection to  this
	      directory. This will be done before --tls-verify is called.  The
	      certificates will	use a temporary	name and will be deleted  when
	      the  tls-verify script returns.  The file	name used for the cer-
	      tificate is available via	the peer_cert environment variable.

       --x509-username-field [ext:]fieldname
	      Field in the X.509 certificate subject to	be used	as  the	 user-
	      name  (default=CN).   Typically,	this  option is	specified with
	      fieldname	as either of the following:

	      --x509-username-field emailAddress
	      --x509-username-field ext:subjectAltName

	      The first	example	uses the value of the "emailAddress" attribute
	      in  the certificate's Subject field as the username.  The	second
	      example uses the ext: prefix to signify that the X.509 extension
	      fieldname	"subjectAltName" be searched for an rfc822Name (email)
	      field to be used as the username.	 In cases where	there are mul-
	      tiple  email  addresses in ext:fieldname,	the last occurrence is

	      When this	option is used,	 the  --verify-x509-name  option  will
	      match against the	chosen fieldname instead of the	Common Name.

	      Please  note:  This  option  has a feature which will convert an
	      all-lowercase fieldname to uppercase characters, e.g., ou	-> OU.
	      A	 mixed-case  fieldname	or  one	having the ext:	prefix will be
	      left as-is.  This	automatic upcasing feature is  deprecated  and
	      will be removed in a future release.

       --tls-remote name (DEPRECATED)
	      Accept  connections  only	 from  a host with X509	name or	common
	      name equal to name.  The remote host must	also  pass  all	 other
	      tests of verification.

	      NOTE:  Because tls-remote	may test against a common name prefix,
	      only use this option when	you are	using OpenVPN with a custom CA
	      certificate  that	 is under your control.	 Never use this	option
	      when your	client certificates are	signed by a third party,  such
	      as a commercial web CA.

	      Name can also be a common	name prefix, for example if you	want a
	      client to	only accept  connections  to  "Server-1",  "Server-2",
	      etc., you	can simply use --tls-remote Server

	      Using a common name prefix is a useful alternative to managing a
	      CRL (Certificate Revocation List)	on the client, since it	allows
	      the  client  to refuse all certificates except for those associ-
	      ated with	designated servers.

	      --tls-remote is a	useful replacement for the --tls-verify	option
	      to  verify  the  remote  host,  because  --tls-remote works in a
	      --chroot environment too.

	      Please also note:	This option is now  deprecated.	  It  will  be
	      removed either in	OpenVPN	v2.4 or	v2.5.  So please make sure you
	      support the new X.509 name formatting described with the	--com-
	      pat-names	option as soon as possible by updating your configura-
	      tions to use --verify-x509-name instead.

       --verify-x509-name name type
	      Accept connections only if a host's X.509	name is	equal to name.
	      The remote host must also	pass all other tests of	verification.

	      Which  X.509  name is compared to	name depends on	the setting of
	      type.  type can be "subject" to match the	 complete  subject  DN
	      (default),  "name"  to  match  a subject RDN or "name-prefix" to
	      match a subject RDN prefix.   Which  RDN	is  verified  as  name
	      depends  on the --x509-username-field option. But	it defaults to
	      the common name (CN), e.g.  a  certificate  with	a  subject  DN
	      "C=KG, ST=NA, L=Bishkek, CN=Server-1" would be matched by:

	      --verify-x509-name  'C=KG,  ST=NA,  L=Bishkek,  CN=Server-1' and
	      --verify-x509-name  Server-1  name  or  you  could  use	--ver-
	      ify-x509-name  Server-  name-prefix if you want a	client to only
	      accept connections to "Server-1",	"Server-2", etc.

	      --verify-x509-name is a useful replacement for the  --tls-verify
	      option  to  verify  the  remote host, because --verify-x509-name
	      works in a --chroot environment without any dependencies.

	      Using a name prefix is a useful alternative to  managing	a  CRL
	      (Certificate Revocation List) on the client, since it allows the
	      client to	refuse all certificates	except	for  those  associated
	      with designated servers.

	      NOTE: Test against a name	prefix only when you are using OpenVPN
	      with a custom CA certificate that	is under your control.	 Never
	      use  this	 option	 with type "name-prefix" when your client cer-
	      tificates	are signed by a	third party, such as a commercial  web

       --x509-track attribute
	      Save peer	X509 attribute value in	environment for	use by plugins
	      and management interface.	 Prepend a '+' to  attribute  to  save
	      values  from  full  cert	chain.	 Values	 will  be  encoded  as
	      X509_<depth>_<attribute>=<value>.	 Multiple --x509-track options
	      can be defined to	track multiple attributes.  Not	available with

       --ns-cert-type client|server
	      Require that  peer  certificate  was  signed  with  an  explicit
	      nsCertType designation of	"client" or "server".

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	with is	a designated server.

	      See the easy-rsa/build-key-server	script for an example  of  how
	      to  generate  a  certificate  with  the  nsCertType field	set to

	      If the server certificate's nsCertType field is set to "server",
	      then the clients can verify this with --ns-cert-type server.

	      This  is	an  important security precaution to protect against a
	      man-in-the-middle	attack where an	authorized client attempts  to
	      connect  to  another  client  by	impersonating the server.  The
	      attack is	easily prevented by having clients verify  the	server
	      certificate using	any one	of --ns-cert-type, --verify-x509-name,
	      or --tls-verify.

       --remote-cert-ku	v...
	      Require that peer	certificate was	signed with  an	 explicit  key

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	to is a	designated server.

	      The key usage should be encoded in hex, more than	one key	 usage
	      can be specified.

       --remote-cert-eku oid
	      Require  that  peer  certificate	was  signed  with  an explicit
	      extended key usage.

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	to is a	designated server.

	      The  extended  key  usage	 should	be encoded in oid notation, or
	      OpenSSL symbolic representation.

       --remote-cert-tls client|server
	      Require that peer	certificate was	signed with  an	 explicit  key
	      usage and	extended key usage based on RFC3280 TLS	rules.

	      This is a	useful security	option for clients, to ensure that the
	      host they	connect	to is a	designated server.

	      The   --remote-cert-tls	client	 option	  is   equivalent   to
	      --remote-cert-ku	80  08	88  --remote-cert-eku  "TLS Web	Client

	      The key usage is digitalSignature	and/or keyAgreement.

	      The   --remote-cert-tls	server	 option	  is   equivalent   to
	      --remote-cert-ku a0 88 --remote-cert-eku "TLS Web	Server Authen-

	      The key usage is digitalSignature	and ( keyEncipherment or keyA-
	      greement ).

	      This  is	an  important security precaution to protect against a
	      man-in-the-middle	attack where an	authorized client attempts  to
	      connect  to  another  client  by	impersonating the server.  The
	      attack is	easily prevented by having clients verify  the	server
	      certificate   using   any	  one	of  --remote-cert-tls,	--ver-
	      ify-x509-name, or	--tls-verify.

       --crl-verify crl	['dir']
	      Check peer certificate against the file crl in PEM format.

	      A	CRL (certificate revocation list) is used  when	 a  particular
	      key is compromised but when the overall PKI is still intact.

	      Suppose  you had a PKI consisting	of a CA, root certificate, and
	      a	number of client certificates.	Suppose	a laptop computer con-
	      taining  a client	key and	certificate was	stolen.	 By adding the
	      stolen certificate to the	CRL file, you could reject any connec-
	      tion  which  attempts  to	 use  it, while	preserving the overall
	      integrity	of the PKI.

	      The only time when it would be necessary to rebuild  the	entire
	      PKI from scratch would be	if the root certificate	key itself was

	      If the optional dir flag is specified, enable a  different  mode
	      where  crl  is  a	 directory  containing	files named as revoked
	      serial numbers (the files	may be empty, the contents  are	 never
	      read).  If a client requests a connection, where the client cer-
	      tificate serial number (decimal string) is the name  of  a  file
	      present in the directory,	it will	be rejected.

	      Note:  As	 the crl file (or directory) is	read every time	a peer
	      connects,	if you are dropping root privileges with --user,  make
	      sure that	this user has sufficient privileges to read the	file.

   SSL Library information:
	      (Standalone) Show	all cipher algorithms to use with the --cipher

	      (Standalone) Show	all message digest algorithms to use with  the
	      --auth option.

	      (Standalone)  Show  all  TLS  ciphers  supported	by  the	crypto
	      library.	OpenVPN	uses TLS to secure the control	channel,  over
	      which  the  keys that are	used to	protect	the actual VPN traffic
	      are exchanged.  The TLS ciphers  will  be	 sorted	 from  highest
	      preference (most secure) to lowest.

	      Be  aware	 that whether a	cipher suite in	this list can actually
	      work depends on the specific setup  of  both  peers  (e.g.  both
	      peers  must  support  the	cipher,	and an ECDSA cipher suite will
	      not work if you are using	an RSA certificate, etc.).

	      (Standalone)  Show  currently  available	hardware-based	crypto
	      acceleration engines supported by	the OpenSSL library.

   Generate a random key:
       Used only for non-TLS static key	encryption mode.

	      (Standalone)  Generate  a	 random	 key  to  be  used as a	shared
	      secret, for use with the --secret	option.	  This	file  must  be
	      shared  with the peer over a pre-existing	secure channel such as

       --secret	file
	      Write key	to file.

   TUN/TAP persistent tunnel config mode:
       Available with linux 2.4.7+.  These options comprise a standalone  mode
       of OpenVPN which	can be used to create and delete persistent tunnels.

	      (Standalone)  Create a persistent	tunnel on platforms which sup-
	      port them	such as	Linux.	Normally TUN/TAP  tunnels  exist  only
	      for  the period of time that an application has them open.  This
	      option takes advantage of	the TUN/TAP driver's ability to	 build
	      persistent  tunnels that live through multiple instantiations of
	      OpenVPN and die only when	they are deleted  or  the  machine  is

	      One  of the advantages of	persistent tunnels is that they	elimi-
	      nate the need for	separate --up and --down scripts  to  run  the
	      appropriate  ifconfig(8)	and route(8) commands.	These commands
	      can be placed in the the same shell script which starts or  ter-
	      minates an OpenVPN session.

	      Another  advantage is that open connections through the TUN/TAP-
	      based tunnel will	not be reset if	 the  OpenVPN  peer  restarts.
	      This can be useful to provide uninterrupted connectivity through
	      the tunnel in the	event of a DHCP	reset of the peer's public  IP
	      address (see the --ipchange option above).

	      One  disadvantage	 of persistent tunnels is that it is harder to
	      automatically configure their  MTU  value	 (see  --link-mtu  and
	      --tun-mtu	above).

	      On some platforms	such as	Windows, TAP-Win32 tunnels are persis-
	      tent by default.

	      (Standalone) Remove a persistent tunnel.

       --dev tunX | tapX
	      TUN/TAP device

       --user user
	      Optional user to be owner	of this	tunnel.

       --group group
	      Optional group to	be owner of this tunnel.

   Windows-Specific Options:
       --win-sys path
	      Set the Windows system directory pathname	to  use	 when  looking
	      for  system  executables	such  as  route.exe and	netsh.exe.  By
	      default, if this directive is not	specified,  OpenVPN  will  use
	      the SystemRoot environment variable.

	      This  option have	changed	behaviour in OpenVPN 2.3.  Earlier you
	      had to define --win-sys env to use  the  SystemRoot  environment
	      variable,	 otherwise  it	defaulted  to  C:\WINDOWS.   It	is not
	      needed to	use the	env keyword any	more,  and  it	will  just  be
	      ignored.	A warning is logged when this is found in the configu-
	      ration file.

       --ip-win32 method
	      When using --ifconfig on Windows,	set the	TAP-Win32  adapter  IP
	      address  and netmask using method.  Don't	use this option	unless
	      you are also using --ifconfig.

	      manual --	Don't set the IP  address  or  netmask	automatically.
	      Instead output a message to the console telling the user to con-
	      figure the adapter manually and indicating the IP/netmask	 which
	      OpenVPN expects the adapter to be	set to.

	      dynamic  [offset]	 [lease-time]  --  Automatically  set  the  IP
	      address and netmask by replying to DHCP query messages generated
	      by  the  kernel.	 This mode is probably the "cleanest" solution
	      for setting the TCP/IP properties	since it uses  the  well-known
	      DHCP  protocol.  There are, however, two prerequisites for using
	      this mode: (1) The TCP/IP	properties for the  TAP-Win32  adapter
	      must  be	set  to	 "Obtain an IP address automatically," and (2)
	      OpenVPN needs to claim an	IP address in the subnet  for  use  as
	      the  virtual DHCP	server address.	 By default in --dev tap mode,
	      OpenVPN will take	the normally unused first address in the  sub-
	      net.   For  example,  if	your  subnet  is  netmask, then OpenVPN will take the	IP address
	      to  use  as the virtual DHCP server address.  In --dev tun mode,
	      OpenVPN will cause the DHCP server to masquerade as if  it  were
	      coming  from the remote endpoint.	 The optional offset parameter
	      is an integer which is > -256 and	< 256 and which	defaults to 0.
	      If offset	is positive, the DHCP server will masquerade as	the IP
	      address at network address + offset.  If offset is negative, the
	      DHCP  server  will  masquerade  as  the  IP address at broadcast
	      address +	offset.	 The Windows ipconfig /all command can be used
	      to show what Windows thinks the DHCP server address is.  OpenVPN
	      will "claim" this	address, so make sure to use a	free  address.
	      Having  said  that,  different OpenVPN instantiations, including
	      different	ends of	the same connection, can share the  same  vir-
	      tual DHCP	server address.	 The lease-time	parameter controls the
	      lease time  of  the  DHCP	 assignment  given  to	the  TAP-Win32
	      adapter,	and is denoted in seconds.  Normally a very long lease
	      time is preferred	because	it prevents routes involving the  TAP-
	      Win32  adapter  from  being  lost	when the system	goes to	sleep.
	      The default lease	time is	one year.

	      netsh -- Automatically set the IP	address	and netmask using  the
	      Windows  command-line  "netsh"  command.	This method appears to
	      work correctly on	Windows	XP but not Windows 2000.

	      ipapi -- Automatically set the IP	address	and netmask using  the
	      Windows IP Helper	API.  This approach does not have ideal	seman-
	      tics, though testing has indicated that it works okay  in	 prac-
	      tice.   If  you  use this	option,	it is best to leave the	TCP/IP
	      properties for the TAP-Win32 adapter  in	their  default	state,
	      i.e. "Obtain an IP address automatically."

	      adaptive -- (Default) Try	dynamic	method initially and fail over
	      to netsh if the DHCP negotiation with the	TAP-Win32 adapter does
	      not  succeed  in	20  seconds.  Such failures have been known to
	      occur when certain third-party firewall  packages	 installed  on
	      the  client  machine block the DHCP negotiation used by the TAP-
	      Win32 adapter.  Note that	if the netsh failover occurs, the TAP-
	      Win32  adapter  TCP/IP  properties  will	be  reset from DHCP to
	      static, and this will cause future OpenVPN  startups  using  the
	      adaptive	mode  to  use  netsh  immediately,  rather than	trying
	      dynamic first.  To "unstick" the adaptive	mode from using	netsh,
	      run  OpenVPN at least once using the dynamic mode	to restore the
	      TAP-Win32	adapter	TCP/IP properties to a DHCP configuration.

       --route-method m
	      Which method m to	use for	adding routes on Windows?

	      adaptive (default) -- Try	IP helper API first.  If  that	fails,
	      fall back	to the route.exe shell command.
	      ipapi -- Use IP helper API.
	      exe -- Call the route.exe	shell command.

       --dhcp-option type [parm]
	      Set  extended  TAP-Win32	TCP/IP	properties,  must be used with
	      --ip-win32 dynamic or --ip-win32 adaptive.  This option  can  be
	      used  to	set  additional	 TCP/IP	 properties  on	 the TAP-Win32
	      adapter, and is particularly useful for configuring  an  OpenVPN
	      client to	access a Samba server across the VPN.

	      DOMAIN name -- Set Connection-specific DNS Suffix.

	      DNS addr -- Set primary domain name server address.  Repeat this
	      option to	set secondary DNS server addresses.

	      WINS addr	-- Set	primary	 WINS  server  address	(NetBIOS  over
	      TCP/IP  Name  Server).  Repeat this option to set	secondary WINS
	      server addresses.

	      NBDD addr	-- Set	primary	 NBDD  server  address	(NetBIOS  over
	      TCP/IP  Datagram	Distribution Server) Repeat this option	to set
	      secondary	NBDD server addresses.

	      NTP addr -- Set primary NTP server address (Network Time	Proto-
	      col).  Repeat this option	to set secondary NTP server addresses.

	      NBT  type	 --  Set  NetBIOS  over	 TCP/IP	 Node  type.  Possible
	      options: 1 = b-node (broadcasts),	 2  =  p-node  (point-to-point
	      name queries to a	WINS server), 4	= m-node (broadcast then query
	      name server), and	8 = h-node (query  name	 server,  then	broad-

	      NBS  scope-id  --	Set NetBIOS over TCP/IP	Scope. A NetBIOS Scope
	      ID provides an extended naming  service  for  the	 NetBIOS  over
	      TCP/IP  (Known  as NBT) module. The primary purpose of a NetBIOS
	      scope ID is to isolate NetBIOS traffic on	a  single  network  to
	      only  those  nodes  with the same	NetBIOS	scope ID.  The NetBIOS
	      scope ID is a character string that is appended to  the  NetBIOS
	      name.  The  NetBIOS scope	ID on two hosts	must match, or the two
	      hosts will not be	able to	communicate. The NetBIOS Scope ID also
	      allows  computers	 to  use  the same computer name, as they have
	      different	scope IDs. The Scope ID	becomes	a part of the  NetBIOS
	      name,  making  the  name	unique.	  (This	description of NetBIOS
	      scopes courtesy of

	      DISABLE-NBT -- Disable Netbios-over-TCP/IP.

	      Note that	if --dhcp-option is pushed via --push to a non-windows
	      client,  the  option  will  be saved in the client's environment
	      before  the  up  script  is  called,  under   the	  name	 "for-

       --tap-sleep n
	      Cause  OpenVPN to	sleep for n seconds immediately	after the TAP-
	      Win32 adapter state is set to "connected".

	      This option is intended to be used to troubleshoot problems with
	      the  --ifconfig  and --ip-win32 options, and is used to give the
	      TAP-Win32	adapter	time to	come up	before Windows IP  Helper  API
	      operations are applied to	it.

	      Output  OpenVPN's	 view  of the system routing table and network
	      adapter list to the syslog or log	file after the TUN/TAP adapter
	      has been brought up and any routes have been added.

	      Block  DNS  servers  on  other  network  adapters	to prevent DNS
	      leaks. This option prevents any application from	accessing  TCP
	      or  UDP  port  53	 except	one inside the tunnel. It uses Windows
	      Filtering	Platform (WFP) and works on Windows Vista or later.

	      This option is considered	unknown	on non-Windows	platforms  and
	      unsupported  on  Windows	XP, resulting in fatal error.  You may
	      want to use --setenv opt or --ignore-unknown-option  (not	 suit-
	      able  for	 Windows  XP) to ignore	said error.  Note that pushing
	      unknown options from server does not trigger fatal errors.

	      Ask Windows to renew the TAP adapter  lease  on  startup.	  This
	      option  is  normally unnecessary,	as Windows automatically trig-
	      gers a DHCP renegotiation	on the TAP adapter when	it  comes  up,
	      however  if  you set the TAP-Win32 adapter Media Status property
	      to "Always Connected", you may need this flag.

	      Ask Windows to release the TAP adapter lease on shutdown.	  This
	      option has the same caveats as --dhcp-renew above.

	      Run  net	stop  dnscache,	net start dnscache, ipconfig /flushdns
	      and ipconfig /registerdns	on  connection	initiation.   This  is
	      known to kick Windows into recognizing pushed DNS	servers.

	      Put  up  a  "press  any  key to continue"	message	on the console
	      prior to OpenVPN program exit.   This  option  is	 automatically
	      used by the Windows explorer when	OpenVPN	is run on a configura-
	      tion file	using the right-click explorer menu.

       --service exit-event [0|1]
	      Should be	used when OpenVPN is being automatically  executed  by
	      another  program	in such	a context that no interaction with the
	      user via display or keyboard is possible.	 In general, end-users
	      should  never need to explicitly use this	option,	as it is auto-
	      matically	added by the OpenVPN  service  wrapper	when  a	 given
	      OpenVPN configuration is being run as a service.

	      exit-event  is  the  name	 of a Windows global event object, and
	      OpenVPN will continuously	monitor	the state of this event	object
	      and exit when it becomes signaled.

	      The  second  parameter indicates the initial state of exit-event
	      and normally defaults to 0.

	      Multiple OpenVPN processes can be	simultaneously	executed  with
	      the  same	 exit-event  parameter.	  In any case, the controlling
	      process can signal exit-event, causing  all  such	 OpenVPN  pro-
	      cesses to	exit.

	      When executing an	OpenVPN	process	using the --service directive,
	      OpenVPN will probably not	have a console window to  output  sta-
	      tus/error	 messages,  therefore  it  is  useful  to use --log or
	      --log-append to write these messages to a	file.

	      (Standalone) Show	available  TAP-Win32  adapters	which  can  be
	      selected	using  the --dev-node option.  On non-Windows systems,
	      the ifconfig(8) command provides similar functionality.

       --allow-nonadmin	[TAP-adapter]
	      (Standalone) Set TAP-adapter to allow access  from  non-adminis-
	      trative  accounts.   If TAP-adapter is omitted, all TAP adapters
	      on the system will be configured to allow	non-admin access.  The
	      non-admin	 access	 setting  will	only persist for the length of
	      time that	the TAP-Win32 device object and	driver remain  loaded,
	      and  will	need to	be re-enabled after a reboot, or if the	driver
	      is unloaded and reloaded.	 This directive	can only be used by an

	      (Standalone)  Show valid subnets for --dev tun emulation.	 Since
	      the TAP-Win32 driver exports an ethernet interface  to  Windows,
	      and since	TUN devices are	point-to-point in nature, it is	neces-
	      sary for the TAP-Win32 driver to impose certain  constraints  on
	      TUN endpoint address selection.

	      Namely,  the  point-to-point endpoints used in TUN device	emula-
	      tion must	be the middle two addresses of a /30  subnet  (netmask

	      (Standalone) Show	OpenVPN's view of the system routing table and
	      network adapter list.

   PKCS#11 Standalone Options:
       --show-pkcs11-ids [provider] [cert_private]
	      (Standalone) Show	PKCS#11	token object list.  Specify  cert_pri-
	      vate as 1	if certificates	are stored as private objects.

	      If  p11-kit  is  present on the system, the provider argument is
	      optional;	if omitted the default	module will be

	      --verb  option  can be used BEFORE this option to	produce	debug-
	      ging information.

   IPv6	Related	Options
       The following options exist to support IPv6 tunneling  in  peer-to-peer
       and client-server mode.	All options are	modeled	after their IPv4 coun-
       terparts, so more detailed explanations given there apply here as  well
       (except for --topology ,	which has no effect on IPv6).

       --ifconfig-ipv6 ipv6addr/bits ipv6remote
	      configure	IPv6 address ipv6addr/bits on the ``tun'' device.  The
	      second parameter is used as route	target for --route-ipv6	if  no
	      gateway is specified.

       --route-ipv6 ipv6addr/bits [gateway] [metric]
	      setup IPv6 routing in the	system to send the specified IPv6 net-
	      work into	OpenVPN's ``tun'' device

       --server-ipv6 ipv6addr/bits
	      convenience-function to enable a number of IPv6 related  options
	      at    once,    namely   --ifconfig-ipv6,	 --ifconfig-ipv6-pool,
	      --tun-ipv6 and --push tun-ipv6  Is  only	accepted  if  ``--mode
	      server'' or ``--server'' is set.

       --ifconfig-ipv6-pool ipv6addr/bits
	      Specify  an IPv6 address pool for	dynamic	assignment to clients.
	      The pool starts at ipv6addr and increments by +1 for  every  new
	      client  (linear  mode).	The /bits setting controls the size of
	      the pool.	 Due to	implementation details,	the pool size must  be
	      between /64 and /112.

       --ifconfig-ipv6-push ipv6addr/bits ipv6remote
	      for  ccd/	 per-client  static  IPv6 interface configuration, see
	      --client-config-dir and --ifconfig-push for more details.

       --iroute-ipv6 ipv6addr/bits
	      for  ccd/	 per-client  static  IPv6  route  configuration,   see
	      --iroute	for  more  details  how	to setup and use this, and how
	      --iroute and --route interact.

       OpenVPN exports a series	of environmental variables for	use  by	 user-
       defined scripts.

   Script Order	of Execution
       --up   Executed after TCP/UDP socket bind and TUN/TAP open.

	      Executed when we have a still untrusted remote peer.

	      Executed	after  connection authentication, or remote IP address

	      Executed in --mode server	mode immediately after client  authen-

	      Executed	after  connection  authentication,  either immediately
	      after, or	some  number  of  seconds  after  as  defined  by  the
	      --route-delay option.

	      Executed right before the	routes are removed.

	      Executed in --mode server	mode on	client instance	shutdown.

       --down Executed after TCP/UDP and TUN/TAP close.

	      Executed in --mode server	mode whenever an IPv4 address/route or
	      MAC address is added to OpenVPN's	internal routing table.

	      Executed in --mode server	mode on	new client  connections,  when
	      the client is still untrusted.

   String Types	and Remapping
       In  certain  cases,  OpenVPN  will  perform  remapping of characters in
       strings.	 Essentially, any characters  outside  the  set	 of  permitted
       characters for each string type will be converted to underbar ('_').

       Q: Why is string	remapping necessary?

       A:  It's	 an important security feature to prevent the malicious	coding
       of strings from	untrusted  sources  to	be  passed  as	parameters  to
       scripts,	saved in the environment, used as a common name, translated to
       a filename, etc.

       Q: Can string remapping be disabled?

       A: Yes, by using	the --no-name-remapping	option,	however	this should be
       considered an advanced option.

       Here  is	a brief	rundown	of OpenVPN's current string types and the per-
       mitted character	class for each string:

       X509 Names: Alphanumeric, underbar ('_'), dash  ('-'),  dot  ('.'),  at
       ('@'),  colon  (':'),  slash  ('/'),  and equal ('=').  Alphanumeric is
       defined as a character which will cause the C library  isalnum()	 func-
       tion to return true.

       Common  Names: Alphanumeric, underbar ('_'), dash ('-'),	dot ('.'), and
       at ('@').

       --auth-user-pass	username: Same as Common  Name,	 with  one  exception:
       starting	 with  OpenVPN	2.0.1,	the  username  is  passed to the OPEN-
       VPN_PLUGIN_AUTH_USER_PASS_VERIFY	plugin in its raw form,	without	string

       --auth-user-pass	 password:  Any	"printable" character except CR	or LF.
       Printable is defined to be a character which will cause the  C  library
       isprint() function to return true.

       --client-config-dir  filename  as derived from common name or username:
       Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except for  "."
       or ".." as standalone strings.  As of 2.0.1-rc6,	the at ('@') character
       has been	added as well for compatibility	with the common	name character

       Environmental variable names: Alphanumeric or underbar ('_').

       Environmental variable values: Any printable character.

       For  all	 cases,	 characters  in	 a string which	are not	members	of the
       legal character class for that string type will be remapped to underbar

   Environmental Variables
       Once  set,  a variable is persisted indefinitely	until it is reset by a
       new value or a restart,

       As of OpenVPN 2.0-beta12, in server mode, environmental	variables  set
       by  OpenVPN are scoped according	to the client objects they are associ-
       ated with, so there should not be any issues with scripts having	access
       to  stale,  previously  set  variables  which refer to different	client

	      Total number of bytes received from client during	 VPN  session.
	      Set prior	to execution of	the --client-disconnect	script.

	      Total  number  of	 bytes sent to client during VPN session.  Set
	      prior to execution of the	--client-disconnect script.

	      The X509 common name of an authenticated client.	Set  prior  to
	      execution	   of	--client-connect,   --client-disconnect,   and
	      --auth-user-pass-verify scripts.

       config Name of first --config file.   Set  on  program  initiation  and
	      reset on SIGHUP.

       daemon Set to "1" if the	--daemon directive is specified, or "0"	other-
	      wise.  Set on program initiation and reset on SIGHUP.

	      Set to "1" if the	--log or --log-append  directives  are	speci-
	      fied,  or	"0" otherwise.	Set on program initiation and reset on

       dev    The actual name of the TUN/TAP device, including a  unit	number
	      if it exists.  Set prior to --up or --down script	execution.

	      On  Windows, the device index of the TUN/TAP adapter (to be used
	      in netsh.exe calls which sometimes just do not work  right  with
	      interface	names).	 Set prior to --up or --down script execution.

	      An  option pushed	via --push to a	client which does not natively
	      support it, such as --dhcp-option	on a non-Windows system,  will
	      be  recorded  to	this  environmental variable sequence prior to
	      --up script execution.

	      The broadcast address for	the virtual ethernet segment which  is
	      derived  from the	--ifconfig option when --dev tap is used.  Set
	      prior to OpenVPN calling the ifconfig or netsh (windows  version
	      of ifconfig) commands which normally occurs prior	to --up	script

	      The local	VPN endpoint IPv6 address specified  in	 the  --ifcon-
	      fig-ipv6 option (first parameter).  Set prior to OpenVPN calling
	      the ifconfig or netsh (windows  version  of  ifconfig)  commands
	      which normally occurs prior to --up script execution.

	      The  prefix  length  of  the  IPv6 network on the	VPN interface.
	      Derived from the /nnn parameter  of  the	IPv6  address  in  the
	      --ifconfig-ipv6  option (first parameter).  Set prior to OpenVPN
	      calling the ifconfig or netsh (windows version of	ifconfig) com-
	      mands which normally occurs prior	to --up	script execution.

	      The  remote  VPN endpoint	IPv6 address specified in the --ifcon-
	      fig-ipv6 option (second parameter).  Set prior to	OpenVPN	 call-
	      ing the ifconfig or netsh	(windows version of ifconfig) commands
	      which normally occurs prior to --up script execution.

	      The local	VPN endpoint IP	address	specified  in  the  --ifconfig
	      option  (first  parameter).   Set	 prior	to OpenVPN calling the
	      ifconfig or netsh	(windows version of ifconfig)  commands	 which
	      normally occurs prior to --up script execution.

	      The  remote  VPN endpoint	IP address specified in	the --ifconfig
	      option (second parameter)	when --dev tun is used.	 Set prior  to
	      OpenVPN calling the ifconfig or netsh (windows version of	ifcon-
	      fig) commands which normally occurs prior	to --up	script	execu-

	      The  subnet  mask	of the virtual ethernet	segment	that is	speci-
	      fied as the second parameter to --ifconfig  when	--dev  tap  is
	      being  used.  Set	prior to OpenVPN calling the ifconfig or netsh
	      (windows version of ifconfig)  commands  which  normally	occurs
	      prior to --up script execution.

	      The  local  virtual IP address for the TUN/TAP tunnel taken from
	      an --ifconfig-push directive if specified, or otherwise from the
	      ifconfig	pool  (controlled  by  the --ifconfig-pool config file
	      directive).  Only	set for	--dev tun tunnels.  This option	is set
	      on  the  server  prior  to execution of the --client-connect and
	      --client-disconnect scripts.

	      The virtual IP netmask for the  TUN/TAP  tunnel  taken  from  an
	      --ifconfig-push  directive  if  specified, or otherwise from the
	      ifconfig pool (controlled	by  the	 --ifconfig-pool  config  file
	      directive).  Only	set for	--dev tap tunnels.  This option	is set
	      on the server prior to execution	of  the	 --client-connect  and
	      --client-disconnect scripts.

	      The  remote virtual IP address for the TUN/TAP tunnel taken from
	      an --ifconfig-push directive if specified, or otherwise from the
	      ifconfig	pool  (controlled  by  the --ifconfig-pool config file
	      directive).  This	option is set on the server prior to execution
	      of the --client-connect and --client-disconnect scripts.

	      The  maximum packet size (not including the IP header) of	tunnel
	      data in UDP tunnel transport mode.  Set prior to --up or	--down
	      script execution.

       local  The  --local  parameter.	Set on program initiation and reset on

	      The local	port number, specified by --port or --lport.   Set  on
	      program initiation and reset on SIGHUP.

	      The  password  provided  by  a  connecting client.  Set prior to
	      --auth-user-pass-verify script execution only when  the  via-env
	      modifier	is  specified,	and deleted from the environment after
	      the script returns.

       proto  The --proto parameter.  Set on program initiation	and  reset  on

	      The  --remote parameter.	Set on program initiation and reset on

	      The remote port number, specified	by --port or --rport.  Set  on
	      program initiation and reset on SIGHUP.

	      The pre-existing default IP gateway in the system	routing	table.
	      Set prior	to --up	script execution.

	      The default gateway used by --route  options,  as	 specified  in
	      either  the  --route-gateway  option  or the second parameter to
	      --ifconfig when --dev tun	 is  specified.	  Set  prior  to  --up
	      script execution.

	      A	 set of	variables which	define each route to be	added, and are
	      set prior	to --up	script execution.

	      parm will	be one of "network", "netmask",	 "gateway",  or	 "met-

	      n	is the OpenVPN route number, starting from 1.

	      If  the  network	or  gateway are	resolvable DNS names, their IP
	      address translations will	be recorded rather than	their names as
	      denoted on the command line or configuration file.

	      A	set of variables which define each IPv6	route to be added, and
	      are set prior to --up script execution.

	      parm will	be one of "network" or "gateway"  ("netmask"  is  con-
	      tained  as  "/nnn"  in  the  route_ipv6_network_{n}, unlike IPv4
	      where it is passed in a separate environment variable).

	      n	is the OpenVPN route number, starting from 1.

	      If the network or	gateway	are resolvable	DNS  names,  their  IP
	      address translations will	be recorded rather than	their names as
	      denoted on the command line or configuration file.

	      Temporary	file name containing the client	certificate upon  con-
	      nection.	Useful in conjunction with --tls-verify

	      Set  to  "init"  or "restart" prior to up/down script execution.
	      For more information, see	documentation for --up.

	      Prior to execution of any	script,	this variable is  set  to  the
	      type  of	script being run.  It can be one of the	following: up,
	      down,  ipchange,	route-up,  tls-verify,	auth-user-pass-verify,
	      client-connect,  client-disconnect, or learn-address.  Set prior
	      to execution of any script.

       signal The reason for exit or restart.  Can be one of sigusr1,  sighup,
	      sigterm,	sigint,	 inactive  (controlled	by --inactive option),
	      ping-exit	(controlled by --ping-exit option), ping-restart (con-
	      trolled  by  --ping-restart option), connection-reset (triggered
	      on TCP connection	reset),	error, or  unknown  (unknown  signal).
	      This variable is set just	prior to down script execution.

	      Client  connection timestamp, formatted as a human-readable time
	      string.  Set prior to execution of the --client-connect script.

	      The duration (in seconds)	of the client  session	which  is  now
	      disconnecting.   Set  prior to execution of the --client-discon-
	      nect script.

	      Client  connection  timestamp,  formatted	 as  a	unix   integer
	      date/time	value.	Set prior to execution of the --client-connect

	      Contains the certificate	SHA1  fingerprint/digest  hash	value,
	      where  n	is  the	 verification level.  Only set for TLS connec-
	      tions.  Set prior	to execution of	--tls-verify script.

	      A	series of certificate fields from the remote peer, where n  is
	      the  verification	 level.	  Only	set  for TLS connections.  Set
	      prior to execution of --tls-verify script.

	      The serial number	of the certificate from	the remote peer, where
	      n	is the verification level.  Only set for TLS connections.  Set
	      prior to execution of --tls-verify script. This is in  the  form
	      of  a  decimal  string  like  "933971680", which is suitable for
	      doing serial-based OCSP queries (with OpenSSL,  do  not  prepend
	      "0x"  to	the  string) If	something goes wrong while reading the
	      value from the certificate it will be an empty string,  so  your
	      code	should	    check      that.	  See	  the	  con-
	      trib/OCSP_check/ script for an example.

	      Like tls_serial_{n}, but in hex form (e.g. "12:34:56:78:9A").

	      The MTU of the TUN/TAP device.  Set  prior  to  --up  or	--down
	      script execution.

       trusted_ip (or trusted_ip6)
	      Actual  IP  address  of connecting client	or peer	which has been
	      authenticated.   Set   prior   to	  execution   of   --ipchange,
	      --client-connect,	 and  --client-disconnect  scripts.   If using
	      ipv6 endpoints (udp6, tcp6), trusted_ip6 will be set instead.

	      Actual port number of connecting client or peer which  has  been
	      authenticated.	Set   prior   to   execution   of  --ipchange,
	      --client-connect,	and --client-disconnect	scripts.

       untrusted_ip (or	untrusted_ip6)
	      Actual IP	address	of connecting client or	 peer  which  has  not
	      been  authenticated  yet.	 Sometimes used	to nmap	the connecting
	      host in a	--tls-verify script to ensure it is  firewalled	 prop-
	      erly.	Set   prior   to   execution   of   --tls-verify   and
	      --auth-user-pass-verify scripts.	If using ipv6 endpoints	(udp6,
	      tcp6), untrusted_ip6 will	be set instead.

	      Actual  port  number  of connecting client or peer which has not
	      been authenticated yet.  Set prior to execution of  --tls-verify
	      and --auth-user-pass-verify scripts.

	      The  username  provided  by  a  connecting client.  Set prior to
	      --auth-user-pass-verify script execution only when  the  via-env
	      modifier is specified.

	      An  X509 subject field from the remote peer certificate, where n
	      is the verification level.  Only set for TLS  connections.   Set
	      prior  to	 execution  of	--tls-verify script.  This variable is
	      similar to tls_id_{n} except the component X509  subject	fields
	      are  broken  out,	 and no	string remapping occurs	on these field
	      values (except for remapping of control characters to "_").  For
	      example,	the  following	variables  would be set	on the OpenVPN
	      server  using  the  sample  client  certificate  in  sample-keys
	      (client.crt).   Note  that  the  verification level is 0 for the
	      client certificate and 1 for the CA certificate.


       OpenVPN allows including	files in the main configuration	for the	 --ca,
       --cert,	--dh,  --extra-certs, --key, --pkcs12, --secret	and --tls-auth

       Each inline file	started	by the line <option> and  ended	 by  the  line

       Here is an example of an	inline file usage

	   -----END CERTIFICATE-----

       When using the inline file feature with --pkcs12	the inline file	has to
       be base64 encoded. Encoding of a	.p12 file into base64 can be done  for
       example with OpenSSL by running openssl base64 -in input.p12

       SIGHUP Cause  OpenVPN  to  close	 all  TUN/TAP and network connections,
	      restart, re-read the configuration file  (if  any),  and	reopen
	      TUN/TAP and network connections.

	      Like SIGHUP, except don't	re-read	configuration file, and	possi-
	      bly don't	close and reopen TUN/TAP device,  re-read  key	files,
	      preserve	local  IP  address/port,  or  preserve	most  recently
	      authenticated remote IP  address/port  based  on	--persist-tun,
	      --persist-key,   --persist-local-ip,   and   --persist-remote-ip
	      options respectively (see	above).

	      This signal may also be internally generated by a	timeout	condi-
	      tion, governed by	the --ping-restart option.

	      This signal, when	combined with --persist-remote-ip, may be sent
	      when the underlying parameters of	the host's  network  interface
	      change  such as when the host is a DHCP client and is assigned a
	      new IP address.  See --ipchange above for	more information.

	      Causes OpenVPN to	display	its current statistics (to the	syslog
	      file if --daemon is used,	or stdout otherwise).

	      Causes OpenVPN to	exit gracefully.

       If you are running Linux	2.4.7 or higher, you probably have the TUN/TAP
       driver already installed.  If so, there are still a few things you need
       to do:

       Make device: mknod /dev/net/tun c 10 200

       Load driver: modprobe tun

       Prior  to  running these	examples, you should have OpenVPN installed on
       two machines with network connectivity between them.  If	you  have  not
       yet installed OpenVPN, consult the INSTALL file included	in the OpenVPN

   TUN/TAP Setup:
       If you are using	Linux 2.4 or higher, make the tun device node and load
       the tun module:

	      mknod /dev/net/tun c 10 200

	      modprobe tun

       If  you	installed from RPM, the	mknod step may be omitted, because the
       RPM install does	that for you.

       Only Linux 2.4 and newer	are supported.

       For  other  platforms,  consult	the  INSTALL  file   at	  http://open- for	more information.

   Firewall Setup:
       If firewalls exist between the two machines, they should	be set to for-
       ward UDP	port 1194 in both directions.  If you do not have control over
       the  firewalls  between	the two	machines, you may still	be able	to use
       OpenVPN by adding --ping	15 to each of the openvpn commands used	 below
       in  the	examples  (this	will cause each	peer to	send out a UDP ping to
       its remote peer once every 15 seconds which will	 cause	many  stateful
       firewalls  to  forward  packets	in both	directions without an explicit
       firewall	rule).

       If you are using	a Linux	iptables-based firewall, you may need to enter
       the following command to	allow incoming packets on the TUN device:

	      iptables -A INPUT	-i tun+	-j ACCEPT

       See  the	 firewalls  section  below for more information	on configuring
       firewalls for use with OpenVPN.

   VPN Address Setup:
       For purposes of our example, our	two machines will be called  bob.exam-	and	If you are constructing	a VPN over the
       internet, then replace and  with  the
       internet	 hostname  or IP address that each machine will	use to contact
       the other over the internet.

       Now we will choose the tunnel endpoints.	 Tunnel	endpoints are  private
       IP  addresses  that  only have meaning in the context of	the VPN.  Each
       machine will use	the tunnel endpoint of the other machine to access  it
       over  the VPN.  In our example, the tunnel endpoint for
       will be	and for,

       Once the	VPN is established, you	 have  essentially  created  a	secure
       alternate  path	between	 the two hosts which is	addressed by using the
       tunnel endpoints.  You can control which	network	traffic	passes between
       the hosts (a) over the VPN or (b) independently of the VPN, by choosing
       whether to use (a) the VPN endpoint address or (b) the public  internet
       address,	to access the remote host. For example if you are on bob.exam- and you wish to connect to  via  ssh  without
       using  the  VPN (since ssh has its own built-in security) you would use
       the command ssh  However in the same	scenario,  you
       could  also  use	the command telnet to create a	telnet session
       with over the VPN, that would use the VPN  to	secure
       the session rather than ssh.

       You can use any address you wish	for the	tunnel endpoints but make sure
       that they are private addresses (such as	those that begin  with	10  or
       192.168)	 and that they are not part of any existing subnet on the net-
       works of	either peer, unless you	are bridging.  If you use  an  address
       that  is	 part of your local subnet for either of the tunnel endpoints,
       you will	get a weird feedback loop.

   Example 1: A	simple tunnel without security
       On bob:

	      openvpn  --remote   --dev   tun1   --ifconfig	--verb 9

       On alice:

	      openvpn  --remote	--dev tun1 --ifconfig --verb 9

       Now verify the tunnel is	working	by pinging across the tunnel.

       On bob:


       On alice:


       The --verb 9 option will	produce	verbose	output,	similar	 to  the  tcp-
       dump(8) program.	 Omit the --verb 9 option to have OpenVPN run quietly.

   Example  2:	A  tunnel  with	 static-key  security (i.e. using a pre-shared
       First build a static key	on bob.

	      openvpn --genkey --secret	key

       This command will build a random	key file called	key (in	ascii format).
       Now  copy key to	alice over a secure medium such	as by using the	scp(1)

       On bob:

	      openvpn  --remote   --dev   tun1   --ifconfig	--verb 5 --secret key

       On alice:

	      openvpn  --remote	--dev tun1 --ifconfig --verb 5	--secret key

       Now verify the tunnel is	working	by pinging across the tunnel.

       On bob:


       On alice:


   Example 3: A	tunnel with full TLS-based security
       For this	test, we will designate	bob as the TLS client and alice	as the
       TLS  server.   Note  that client	or server designation only has meaning
       for the TLS subsystem. It has no	 bearing  on  OpenVPN's	 peer-to-peer,
       UDP-based communication model.

       First,  build  a	 separate  certificate/key pair	for both bob and alice
       (see above where	--cert is discussed for	more  info).   Then  construct
       Diffie  Hellman	parameters (see	above where --dh is discussed for more
       info).	You  can  also	use  the  included  test   files   client.crt,
       client.key, server.crt, server.key and ca.crt.  The .crt	files are cer-
       tificates/public-keys, the .key files are private keys, and ca.crt is a
       certification  authority	who has	signed both client.crt and server.crt.
       For Diffie Hellman parameters you can use the included file dh1024.pem.
       Note  that  all	client,	server,	and certificate	authority certificates
       and keys	included in the	OpenVPN	distribution are totally insecure  and
       should be used for testing only.

       On bob:

	      openvpn	--remote   --dev  tun1  --ifconfig	--tls-client  --ca  ca.crt  --cert  client.crt
	      --key client.key --reneg-sec 60 --verb 5

       On alice:

	      openvpn  --remote	--dev tun1 --ifconfig	--tls-server  --dh  dh1024.pem	--ca   ca.crt	--cert
	      server.crt --key server.key --reneg-sec 60 --verb	5

       Now verify the tunnel is	working	by pinging across the tunnel.

       On bob:


       On alice:


       Notice  the --reneg-sec 60 option we used above.	 That tells OpenVPN to
       renegotiate the data channel keys every minute.	Since we used --verb 5
       above, you will see status information on each new key negotiation.

       For  production	operations, a key renegotiation	interval of 60 seconds
       is probably too frequent.  Omit the --reneg-sec 60 option to use	 Open-
       VPN's default key renegotiation interval	of one hour.

       Assuming	 you  can  ping	across the tunnel, the next step is to route a
       real subnet over	the secure tunnel.  Suppose that bob  and  alice  have
       two  network  interfaces	 each,	one connected to the internet, and the
       other to	a private network.  Our	goal is	to securely connect both  pri-
       vate networks.  We will assume that bob's private subnet	is
       and alice's is

       First, ensure that IP forwarding	is enabled on both peers.   On	Linux,
       enable routing:

	      echo 1 > /proc/sys/net/ipv4/ip_forward

       and enable TUN packet forwarding	through	the firewall:

	      iptables -A FORWARD -i tun+ -j ACCEPT

       On bob:

	      route add	-net netmask gw

       On alice:

	      route add	-net netmask gw

       Now any machine on the subnet can access any	machine	on the subnet over the secure tunnel (or vice versa).

       In a production environment, you	could put the route  command(s)	 in  a
       script and execute with the --up	option.

       OpenVPN's usage of a single UDP port makes it fairly firewall-friendly.
       You should add an entry to your firewall	rules to allow incoming	 Open-
       VPN packets.  On	Linux 2.4+:

	      iptables -A INPUT	-p udp -s --dport 1194 -j ACCEPT

       This  will  allow  incoming packets on UDP port 1194 (OpenVPN's default
       UDP port) from an OpenVPN peer at

       If you are using	HMAC-based packet authentication (the default  in  any
       of  OpenVPN's  secure  modes),  having  the  firewall  filter on	source
       address can be considered optional, since HMAC packet authentication is
       a  much	more  secure  method of	verifying the authenticity of a	packet
       source.	In that	case:

	      iptables -A INPUT	-p udp --dport 1194 -j ACCEPT

       would be	adequate and would not render the host inflexible with respect
       to its peer having a dynamic IP address.

       OpenVPN	also works well	on stateful firewalls.	In some	cases, you may
       not need	to add any static rules	to the firewall	list if	you are	 using
       a  stateful  firewall  that knows how to	track UDP connections.	If you
       specify --ping n, OpenVPN will be guaranteed to send a  packet  to  its
       peer  at	 least	once  every n seconds.	If n is	less than the stateful
       firewall	connection timeout, you	can  maintain  an  OpenVPN  connection
       indefinitely without explicit firewall rules.

       You  should also	add firewall rules to allow incoming IP	traffic	on TUN
       or TAP devices such as:

	      iptables -A INPUT	-i tun+	-j ACCEPT

       to allow	input packets from tun devices,

	      iptables -A FORWARD -i tun+ -j ACCEPT

       to allow	input packets from tun devices to be forwarded to other	 hosts
       on the local network,

	      iptables -A INPUT	-i tap+	-j ACCEPT

       to allow	input packets from tap devices,	and

	      iptables -A FORWARD -i tap+ -j ACCEPT

       to  allow input packets from tap	devices	to be forwarded	to other hosts
       on the local network.

       These rules are secure if  you  use  packet  authentication,  since  no
       incoming	packets	will arrive on a TUN or	TAP virtual device unless they
       first pass an HMAC authentication test.


       For a more comprehensive	guide to setting up OpenVPN  in	 a  production
       setting,	see the	OpenVPN	HOWTO at

       For  a  description  of OpenVPN's underlying protocol, see http://open-

       OpenVPN's web site is at

       Go here to download the latest version of  OpenVPN,  subscribe  to  the
       mailing lists, read the mailing list archives, or browse	the SVN	repos-

       Report all bugs to the OpenVPN team <>.

       dhcpcd(8), ifconfig(8), openssl(1), route(8), scp(1) ssh(1)

       This product includes software  developed  by  the  OpenSSL  Project  ( )

       For     more	information	on     the     TLS    protocol,	   see

       For more	information on	the  LZO  real-time  compression  library  see

       Copyright (C) 2002-2010 OpenVPN Technologies, Inc. This program is free
       software; you can redistribute it and/or	modify it under	the  terms  of
       the GNU General Public License version 2	as published by	the Free Soft-
       ware Foundation.

       James Yonan <>

			       17 November 2008			    openvpn(8)


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